Fluorine-containing ether compound, lubricant for magnetic recording medium, and magnetic recording medium

ABSTRACT

There is provided a fluorine-containing ether compound represented by the following formula. R 1 —R 2 —CH 2 —R 3 —CH 2 —OCH 2 CH(OH)CH 2 O—CH 2 —R 3 —CH 2 —R 4 —R 5  (in the formula. R 3  represents a perfluoropolyether chain; R 2  and R 4  represent a divalent linking group having a polar group; R 1  and R 5  represent a terminal group bonded to an oxygen atom of R 2  or R 4 ; and at least one of R 1  and R 5  is any one selected from the group consisting of an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having 3 to 8 carbon atoms, an aromatic hydrocarbon-containing group, and an aromatic heterocycle-containing group).

TECHNICAL FIELD

The present invention relates to a fluorine-containing ether compound, alubricant for a magnetic recording medium and a magnetic recordingmedium.

Priority is claimed on Japanese Patent Application No. 2019-232040,filed Dec. 23, 2019, the content of which is incorporated herein byreference.

BACKGROUND ART

The development of magnetic recording media suitable for high recordingdensities has progressed in order to improve the recording densities ofmagnetic recording/reproducing devices.

As a conventional magnetic recording medium, there has been a magneticrecording medium in which a recording layer is formed on a substrate anda protective layer made of carbon or the like is formed on the recordinglayer. The protective layer protects information recorded in therecording layer and enhances the slidability of a magnetic head.However, sufficient durability of the magnetic recording medium cannotbe obtained by simply providing the protective layer on the recordinglayer. Therefore, generally, a lubricant is applied to the surface ofthe protective layer to form a lubricating layer.

As a lubricant that is used for forming a lubricating layer in amagnetic recording medium, for example, a lubricant containing acompound having a polar group such as a hydroxyl group or an amino groupat a terminal of a fluorine-based polymer having a repeating structurecontaining CF₂ has been proposed.

For example. Patent Document 1 and Patent Document 2 disclose a compoundin which a perfluoropolyether is bonded to both sides of an aliphatichydrocarbon chain having a hydroxyl group present in the center of amolecule.

Patent Document 3 discloses a fluorine-containing ether compound inwhich a terminal group having an aromatic ring is bonded to bothterminals of a perfluoropolyether chain via divalent linking groupshaving a polar group.

Patent Document 4 discloses a fluorine-containing ether compound inwhich an alkenyl group or an alkynyl group is bonded to both terminalsof a perfluoropolyether chain via divalent linking groups having a polargroup.

Patent Document 5 discloses a fluorine-containing ether compound inwhich a group having a heterocycle is bonded to both terminals of aperfluoropolyether chain via divalent linking groups having a polargroup.

CITATION LIST Patent Literature

-   [Patent Document 1]    -   U.S. Pat. No. 9,805,755-   [Patent Document 2]    -   PCT International Publication No. WO 2016/084781-   [Patent Document 3]    -   Japanese Unexamined Patent Application. First Publication No.        2010-143855-   [Patent Document 4]    -   PCT International Publication No. WO 2018/139058-   [Patent Document 5]    -   PCT International Publication No. WO 2018/139174

SUMMARY OF INVENTION Technical Problem

There is a demand for a further decrease in a floating height of amagnetic head in magnetic recording/reproducing devices. This requires afurther decrease in the thickness of a lubricating layer in magneticrecording media.

However, generally, if the thickness of the lubricating layer isreduced, the adhesion of the lubricating layer is lowered, and chemicalsubstance resistance and wear resistance of magnetic recording mediatend to be lowered.

The present invention has been made in view of the above circumstances,and an object of the present invention is to provide afluorine-containing ether compound which can form a lubricating layerhaving excellent adhesion and favorable chemical substance resistanceand wear resistance even if the thickness is thin, and can be suitablyused as a material for a lubricant for a magnetic recording medium.

In addition, another object of the present invention is to provide alubricant for a magnetic recording medium which contains thefluorine-containing ether compound of the present invention and whichcan form a lubricating layer having excellent adhesion and favorablechemical substance resistance and wear resistance.

In addition, still another object of the present invention is to providea magnetic recording medium in which a lubricating layer containing thefluorine-containing ether compound of the present invention is providedand which has excellent reliability and durability.

Solution to Problem

The present invention includes the following first aspect.

A fluorine-containing ether compound represented by the followingFormula (1):

R¹—R²—CH₂—R³—CH₂—OCH₂CH(OH)CH₂O—CH₂—R³—CH₂—R⁴—R⁵  (1)

(in Formula (1), R³ represents a perfluoropolyether chain: R² and R⁴represent a divalent linking group having a polar group, and may be thesame as or different from each other. R¹ and R⁵ represent a terminalgroup bonded to an oxygen atom of R² or R⁴, and may be the same as ordifferent from each other; and at least one of R¹ and R⁵ is any oneselected from the group consisting of an alkenyl group having 2 to 8carbon atoms, an alkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup).

The compound of the first aspect of the present invention preferably hasthe following features [2] to [15]. It is preferable to combine two ormore of these features.

[2] The fluorine-containing ether compound according to [1].

wherein, in Formula (1). R¹ and R⁵ each represent an alkenyl grouphaving 2 to 5 carbon atoms or an alkynyl group having 3 to 5 carbonatoms.

[3] The fluorine-containing ether compound according to [1].

wherein, in Formula (1). R¹ and R⁵ are each independently any oneselected from the group consisting of an allyl group, a 3-butenyl group,a 4-pentenyl group, and a propargyl group.

[4] The fluorine-containing ether compound according to [1].

wherein, in Formula (1). R¹ and R⁵ are an aromaticheterocycle-containing group.

[5] The fluorine-containing ether compound according to [1],

wherein, in Formula (1). R¹ and R⁵ are each independently any oneselected from the group consisting of a group containing a thiophenering, a group containing a thiazole ring, and a group containing apyrazole ring.

[6] The fluorine-containing ether compound according to any one of [1]to [5].

wherein the polar group is a hydroxyl group.

[7] The fluorine-containing ether compound according to [6].

wherein, in Formula (1), the total number of a hydroxyl group containedin R² and a hydroxyl group contained in R⁴ is 2 to 5.

[8] The fluorine-containing ether compound according to any one of [1]to [7].

wherein, in Formula (1), R² and R⁴ contain 1 to 3 linking groupsrepresented by the following Formula (2):

—CH₂CH(OH)CH₂—  (2)

[9] The fluorine-containing ether compound according to [8].

wherein, in Formula (1), R² and R⁴ are a linking group represented bythe following Formula (2-1):

—O—X—(Y¹X)_(a)—Y²—  (2-1)

(in Formula (2-1), a represents an integer of 0 to 2; X representsFormula (2); Y¹ represents any one selected from the group consisting of—O—, —CH₂—, —CH₂O—, and —OCH₂—; and Y² represents —O— or —CH₂O—).

[10] The fluorine-containing ether compound according to [9],

wherein, in Formula (2-1). Y¹ and Y² are —O—.

[11] The fluorine-containing ether compound according to any one of [1]to [10].

wherein, in Formula (1). R³ is any one selected from the groupconsisting of perfluoropolyether chains represented by the followingFormulae (3) to (5):

—CF₂(OCF₂CF₂)_(b)—(OCF₂)_(c)—OCF₂—  (3)

(in Formula (3), b and c indicate an average degree of polymerization, brepresents 1 to 20, and c represents 0 to 20).

—CF₂CF₂—(OCF₂CF₂CF₂)_(d)—OCF₂CF₂—  (4)

(in Formula (4), d indicates an average degree of polymerization, andrepresents 1 to 20), and

—CF₂CF₂CF₂—(OCF₂CF₂CF₂CF₂)_(e)—OCF₂CF₂CF₂—  (5)

(in Formula (5), e indicates an average degree of polymerization, andrepresents 1 to 10).

[12] The fluorine-containing ether compound according to any one of [1]to [11].

wherein, in Formula (1), R¹ and R⁵ are the same.

[13] The fluorine-containing ether compound according to [1].

wherein, in Formula (1), both R¹ and R⁵ are any one selected from thegroup consisting of an alkenyl group having 2 to 8 carbon atoms, analkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup. R¹ and R⁵ are different from each other, and at least one of R¹and R⁵ is any one selected from the group consisting of an allyl group,a 3-butenyl group, and a 4-pentenyl group.

[14] The fluorine-containing ether compound according to [1], which isany of compounds represented by the following Formulae (A) to (P):

(in Formula (A), ma1, ma2, na1, and na2 indicate an average degree ofpolymerization, ma1 and ma2 represent 1 to 20, and na1 and na2 represent0 to 20).

(in Formula (B), mb1, mb2, nb1, and nb2 indicate an average degree ofpolymerization, mb1 and mb2 represent 1 to 20, and nb1 and nb2 represent0 to 20).

(in Formula (C), mc1, mc2, nc1, and nc2 indicate an average degree ofpolymerization, mc1 and mc2 represent 1 to 20, and nc1 and nc2 represent0 to 20), and

(in Formula (D), md1, md2, nd1, and nd2 indicate an average degree ofpolymerization, md1 and md2 represent 1 to 20, and nd1 and nd2 represent0 to 20).

(in Formula (E), me1, me2, ne1, and ne2 indicate an average degree ofpolymerization, me1 and me2 represent 1 to 20, and ne1 and ne2 represent0 to 20).

(in Formula (F), mf1, mf2, nf1, and nf2 indicate an average degree ofpolymerization, mf1 and mf2 represent 1 to 20, and nf1 and nf2 represent0 to 20).

(in Formula (G), mg1, mg2, ng1, and ng2 indicate an average degree ofpolymerization, mg1 and mg2 represent 1 to 20, and ng1 and ng2 represent0 to 20), and

(in Formula (H), mh1, mh2, nh1, and nh2 indicate an average degree ofpolymerization, mh1 and mh2 represent 1 to 20, and nh1 and nh2 represent0 to 20).

(in Formula (1), mi1, mi2, ni1, and ni2 indicate an average degree ofpolymerization, mi1 and mi2 represent 1 to 20, and ni1 and ni2 represent0 to 20).

(in Formula (J), mj1, mj2, nj1, and nj2 indicate an average degree ofpolymerization, mj1 and mj2 represent 1 to 20, and nj1 and nj2 represent0 to 20).

(in Formula (K), mk1, mk2, nk1, and nk2 indicate an average degree ofpolymerization, mk1 and mk2 represent 1 to 20, and nk1 and nk2 represent0 to 20), and

(in Formula (L), ml1, ml2, nl1, and nl2 indicate an average degree ofpolymerization, ml1 and ml2 represent 1 to 20, and nl1 and nl2 represent0 to 20).

(in Formula (M), mm1, mm2, nm1, and nm2 indicate an average degree ofpolymerization, mm1 and mm2 represent 1 to 20, and nm1 and nm2 represent0 to 20).

(in Formula (N), mn1, mn2, nn1, and nn2 indicate an average degree ofpolymerization, mn1 and mn2 represent 1 to 20, and nn1 and nn2 represent0 to 20).

(in Formula (O), po1 and po2 indicate an average degree ofpolymerization, and each represent 1 to 20), and

(in Formula (P), qp1 and qp2 indicate an average degree ofpolymerization, and each represent 1 to 10).

[15] The fluorine-containing ether compound according to any one of [1]to [14].

wherein the number-average molecular weight thereof is in a range of 500to 10,000.

A second aspect of the present invention is the following lubricant.

[16] A lubricant for a magnetic recording medium, which contains thefluorine-containing ether compound according to any one of [1] to [15].

A third aspect of the present invention is the following magneticrecording medium.

[17] A magnetic recording medium having at least a magnetic layer, aprotective layer, and a lubricating layer sequentially provided on asubstrate.

wherein the lubricating layer contains the fluorine-containing ethercompound according to any one of [1] to [15].

The magnetic recording medium preferably has the following feature.

[18] The magnetic recording medium according to [17].

wherein the average film thickness of the lubricating layer is 0.5 nm to2.0 nm.

[Advantageous Effects of Invention]

The fluorine-containing ether compound of the present invention is acompound represented by Formula (1) and is suitable as a material for alubricant for a magnetic recording medium.

Since the lubricant for a magnetic recording medium of the presentinvention contains the fluorine-containing ether compound of the presentinvention, it is possible to form a lubricating layer having excellentadhesion and favorable chemical substance resistance and wear resistanceeven if the thickness is thin.

Since the magnetic recording medium of the present invention is providedwith a lubricating layer having excellent adhesion and favorablechemical substance resistance and wear resistance by containing thefluorine-containing ether compound of the present invention, it hasexcellent reliability and durability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a preferableembodiment of a magnetic recording medium of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferable examples of a fluorine-containing ethercompound, a lubricant and a magnetic recording medium of the presentinvention will be described in detail.

Here, the present invention is not limited only to the followingembodiments. In the present invention, for example, the numbers, types,compositions, positions, amounts, ratios, materials, configurations andthe like can be added, omitted, substituted or changed without departingfrom the scope of the present invention.

As a conventional material for a lubricant for a magnetic recordingmedium (hereinafter abbreviated as a “lubricant” in some cases) appliedto the surface of a protective layer, a fluorine-containing ethercompound having a polar group such as a hydroxyl group at a terminal ofa chain structure is preferably used. The polar group in thefluorine-containing ether compound binds to an active site on theprotective layer and improves the adhesiveness (adhesion) of thelubricating layer to the protective layer. For this reason, as amaterial of the lubricant, a fluorine-containing ether compound having apolar group not only at a terminal of a chain structure but also in thechain structure is particularly preferably used.

However, when a thin lubricating layer is formed on a protective layerusing a conventional lubricant, as shown below, it is difficult torealize a lubricating layer having excellent adhesion and favorablechemical substance resistance and wear resistance.

That is, if the adhesiveness of the lubricant to the protective layer(adhesion of the lubricating layer) is insufficient, the lubricantapplied onto the protective layer becomes bulky. Therefore, the coatingof the lubricating layer with respect to the protective layer tends tobe non-uniform. If the coating of the lubricating layer is non-uniform,the chemical substance resistance and wear resistance of the lubricatinglayer become insufficient. Therefore, if the adhesion of the lubricatinglayer is insufficient, sufficient chemical substance resistance and wearresistance cannot be obtained unless the film thickness is increased tomake the coating of the lubricating layer uniform with respect to theprotective layer.

Regarding a method of improving the adhesiveness of the lubricant to theprotective layer (adhesion of the lubricating layer), it is conceivableto use a fluorine-containing ether compound in which polar groups arebonded to a terminal carbon atom of a chain structure, a carbon atombonded to the terminal carbon atom, and other carbon atoms in the chainstructure as a material for a lubricant.

However, in the lubricating layer formed using such afluorine-containing ether compound, if the adhesion to the protectivelayer is too strong, the lubricity may be impaired, and the wearresistance may be insufficient.

The adhesion of the lubricant to the protective layer can be adjusted,for example, by changing a heat treatment temperature in a heattreatment that is performed as necessary after a lubricant containing afluorine-containing ether compound is applied onto a protective layer.Specifically, the adhesion of the lubricant to the protective layerbecomes stronger if the heat treatment temperature is raised, andbecomes weaker if the heat treatment temperature is lowered.

Therefore, if the adhesion of the lubricant to the protective layer istoo strong, the adhesion between the lubricating layer and theprotective layer is weakened by using a method of lowering a heattreatment temperature or the like, the adhesion between the lubricatinglayer and the protective layer is set to have an appropriate strength,and thus the wear resistance of the lubricating layer can be improved.

However, in a lubricating layer formed using a fluorine-containing ethercompound in which polar groups are bonded to a terminal carbon atom of achain structure, a carbon atom bonded to the terminal carbon atom, andother carbon atoms in the chain structure, if the adhesion to theprotective layer is weakened by using the above method or the like, thechemical substance resistance of the lubricating layer deteriorates.This is speculated to be because the proportion of polar groups that arenot involved in binding to the active sites on the protective layeramong polar groups in the fluorine-containing ether compound increases.That is, this is speculated to be because polar groups in thefluorine-containing ether compound that are not involved in binding tothe active sites on the protective layer attract environmentalsubstances that produce contamination substances to the lubricatinglayer, and the chemical substance resistance of the lubricating layerdeteriorates.

Here, the inventors have focused on binding between polar groupscontained in the fluorine-containing ether compound and the active siteson the protective layer, and conducted extensive studies in order torealize a fluorine-containing ether compound in which polar groups thatare not involved in binding to the active sites on the protective layerare unlikely to occur and which can form a lubricating layer havinguniform coating with respect to the protective layer and havingfavorable adhesion and favorable chemical substance resistance and wearresistance.

As a result, they found that a fluorine-containing ether compound inwhich a glycerin structure is disposed in the center of a chainstructure, and a perfluoropolyether chain, a methylene group, a divalentlinking group having a polar group, and a terminal group are bonded inthat order to both sides thereof via a methylene group (—CH₂—), and atleast one terminal group is any one selected from the group consistingof an alkenyl group having 2 to 8 carbon atoms, an alkynyl group having3 to 8 carbon atoms, an aromatic hydrocarbon-containing group, and anaromatic heterocycle-containing group is preferable.

In such a fluorine-containing ether compound, an unsaturated bond iscontained in at least one terminal group. The π bond of the unsaturatedbond contained in at least one terminal group thereof forms aninteraction with a protective film and provides adsorption. Thispromotes the interaction between the hydroxyl group of the glycerinstructure and the polar group of the divalent linking group, and theprotective film. Thus, the hydroxyl group of the glycerin structure, andthe polar group of the divalent linking group are bonded to a pluralityof functional groups (active sites) present on the protective layer. Asa result, it is speculated that the fluorine-containing ether compoundcan form a lubricating layer having favorable adhesion to the protectivelayer.

Moreover, in such a fluorine-containing ether compound, at least oneterminal group is any one selected from the group consisting of analkenyl group having 2 to 8 carbon atoms, an alkynyl group having 3 to 8carbon atoms, an aromatic hydrocarbon-containing group, and an aromaticheterocycle-containing group. Therefore, compared with afluorine-containing ether compound in which polar groups are bonded to aterminal carbon atom of a chain structure, a carbon atom bonded to theterminal carbon atom and other carbon atoms in the chain structure, theinteraction (affinity) with the protective layer is weaker. Therefore,the lubricating layer composed of the fluorine-containing ether compoundis unlikely to have insufficient wear resistance because of the adhesionto the protective layer being too strong.

In addition, in the fluorine-containing ether compound, aperfluoropolyether chain is disposed between a glycerin structuredisposed in the center of the chain structure and two divalent linkinggroups. Therefore, the distance between the hydroxyl group (—OH) of theglycerin structure and the polar group of the divalent linking group isappropriate. Moreover, at least one terminal group is any one selectedfrom the group consisting of an alkenyl group having 2 to 8 carbonatoms, an alkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup. Accordingly, binding to the active site on the protective layerwith the hydroxyl group of the glycerin structure and the polar group ofthe divalent linking group is less likely to be inhibited by adjacentpolar groups. Therefore, both the hydroxyl group of the glycerinstructure and the polar group of the divalent linking group are likelyto be involved in binding to the active sites on the protective layer,and are unlikely to be polar groups that are not involved in binding tothe active sites on the protective layer. Therefore, in thefluorine-containing ether compound, it is possible to reduce the numberof polar groups that are not involved in binding to the active sites onthe protective layer, and it is possible to reduce deterioration of thechemical substance resistance and the occurrence of pickup.

In addition, in the above fluorine-containing ether compound, since thedistance between the hydroxyl group of the glycerin structure and thepolar group of the divalent linking group is appropriate, the hydroxylgroup of the glycerin structure is less likely to aggregate with thepolar group of the divalent linking group. Moreover, both terminals ofeach perfluoropolyether chain are brought into close contact with theprotective layer by the hydroxyl group of the glycerin structure and thepolar group of the divalent linking group. Therefore, thefluorine-containing ether compound applied onto the protective layer isunlikely to be bulky, the fluorine-containing ether compound easily wetsand spreads on the protective layer, and a lubricating layer havinguniform coating is easily obtained. Therefore, the fluorine-containingether compound can form a lubricating layer having favorable chemicalsubstance resistance and wear resistance.

In addition, the inventors confirmed that, when a lubricant containingthe fluorine-containing ether compound is used, it is possible to form alubricating layer having excellent adhesion even if the thickness isthin, and having favorable chemical substance resistance and wearresistance, and completed the present invention.

Hereinafter, preferable examples of a fluorine-containing ethercompound, a lubricant for a magnetic recording medium and a magneticrecording medium of the present invention will be described in detail.Here, the present invention is not limited to the following embodiments.

[Fluorine-Containing Ether Compound]

The fluorine-containing ether compound of the present embodiment isrepresented by the following Formula (1):

R¹—R²—CH₂—R³—CH₂—OCH₂CH(OH)CH₂O—CH₂—R³—CH₂—R⁴—R⁵  (1)

(in Formula (1), R³ represents a perfluoropolyether chain; R² and R⁴represent a divalent linking group having a polar group, and may be thesame as or different from each other; R¹ and R⁵ represent a terminalgroup bonded to an oxygen atom of R² or R⁴, and may be the same as ordifferent from each other; and at least one of R¹ and R⁵ is any oneselected from the group consisting of an alkenyl group having 2 to 8carbon atoms, an alkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup).

As shown in Formula (1), the fluorine-containing ether compound of thepresent embodiment has a structure in which a glycerin structure isdisposed in the center of the chain structure, and a perfluoropolyetherchain represented by R³ (hereinafter abbreviated as “PFPE chain” in somecases), a methylene group, divalent linking groups having a polar grouprepresented by R² and R⁴, and terminal groups represented by R¹ and R⁵are bonded in that order to both sides via a methylene group (—CH₂—). InFormula (1), at least one terminal group of R¹ and R⁵ is any oneselected from the group consisting of an alkenyl group having 2 to 8carbon atoms, an alkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup.

(Glycerin Structure)

In the fluorine-containing ether compound represented by Formula (1),the hydroxyl group (—OH) of the glycerin structure (—OCH₂CH(OH)CH₂O—)disposed in the center of the chain structure adheres thefluorine-containing ether compound and the protective layer to form athin lubricating layer with sufficient coverage.

In addition, oxygen atoms disposed at both terminals of the glycerinstructure form an ether bond (—O—) with methylene groups (—CH₂—)disposed on both sides. These two ether bonds impart appropriateflexibility to the fluorine-containing ether compound represented byFormula (1), and increase the affinity between the hydroxyl group of theglycerin structure and the protective layer.

(PFPE Chain Represented by R³)

In the fluorine-containing ether compound represented by Formula (1),when the lubricant containing the fluorine-containing ether compound ofthe present embodiment is applied onto the protective layer to form alubricating layer, the PFPE chain represented by R³ covers the surfaceof the protective layer, imparts lubricity to the lubricating layer, andreduces the frictional force between the magnetic head and theprotective layer. The PFPE chain is appropriately selected depending onthe performance and the like required for the lubricant containing afluorine-containing ether compound.

Examples of PFPE chains include those composed of perfluoroalkyleneoxide polymers or copolymers. Examples of perfluoroalkylene oxidesinclude perfluoromethylene oxide, perfluoroethylene oxide,perfluoro-n-propylene oxide, and perfluorobutylene oxide.

Specifically, in Formula (1), R³ is preferably any one selected from thegroup consisting of PFPE chains represented by the following Formulae(3) to (5). When R³ is any one selected from the group consisting ofPFPE chains represented by Formulae (3) to (5), a fluorine-containingether compound which can form a lubricating layer having favorablelubricity is obtained. When R³ is any one selected from the groupconsisting of PFPE chains represented by Formulae (3) to (5), the ratioof the number of oxygen atoms (the number of ether bonds (—O—)) to thenumber of carbon atoms in the PFPE chain is appropriate. Therefore, thefluorine-containing ether compound having an appropriate hardness isobtained. Therefore, the fluorine-containing ether compound applied ontothe protective layer is less likely to aggregate on the protectivelayer, and an even thinner lubricating layer can be formed withsufficient coverage. In Formula (1), R³ is particularly preferably aPFPE chain represented by Formula (3) so that the fluorine-containingether compound has appropriate flexibility and thus can form alubricating layer having better chemical substance resistance and wearresistance.

—CF₂—(OCF₂CF₂)_(b)—(CF₂)_(c)—OCF₂—  (3)

(in Formula (3), b and c indicate an average degree of polymerization, brepresents 1 to 20, and c represents 0 to 20).

—CF₂CF₂—(OCF₂CF₂CF₂)_(d)—OCF₂CF₂—  (4)

(in Formula (4), d indicates an average degree of polymerization, andrepresents 1 to 20), and

—CF₂CF₂CF₂—(OCF₂CF₂CF₂CF₂)_(e)—OCF₂CF₂CF₂—  (5)

(in Formula (5), e indicates an average degree of polymerization, andrepresents 1 to 10).

In Formula (3), the arrangement sequence of the repeating units(OCF₂CF₂) and (OCF₂) is not particularly limited. In Formula (3), thenumber b of (OCF₂CF₂) and the number c of (OCF₂) may be the same as ordifferent from each other. The PFPE chain represented by Formula (3) maybe a polymer of (OCF₂CF₂). In addition, the PFPE chain represented byFormula (3) may be any one of a random copolymer, a block copolymer, andan alternating copolymer composed of (OCF₂CF₂) and (OCF₂).

In Formulae (4) and (5), since d which indicates an average degree ofpolymerization is 1 to 20, e is 1 to 10 (or in Formula (3), b is 1 to20, and c is 0 to 20), a fluorine-containing ether compound which canform a lubricating layer having favorable lubricity is obtained. Inaddition, in Formulae (3) to (5), since b, c, and d which indicateaverage degrees of polymerization are 20 or less, and e is 10 or less,the viscosity of the fluorine-containing ether compound does not becometoo high, and a lubricant containing the compound is preferable becauseit is easy to apply, b, c, d, and e which indicate average degrees ofpolymerization are preferably 2 to 10 and more preferably 3 to 7 so thatthe fluorine-containing ether compound becomes a compound which easilywets and spreads on the protective layer and allows a lubricating layerhaving a uniform film thickness to be easily obtained.

In the fluorine-containing ether compound represented by Formula (1),two PFPE chains represented by R³ may be the same as or different fromeach other.

(Divalent Linking Groups Having a Polar Group Represented by R² and R⁴)

In the fluorine-containing ether compound represented by Formula (1). R²and R⁴ represent a divalent linking group having a polar group. In thefluorine-containing ether compound represented by Formula (1), since R²and R⁴ have a polar group, when a lubricant containing the compound isused to form a lubricating layer on the protective layer, a suitableinteraction occurs between the lubricating layer and the protectivelayer. The divalent linking group having a polar group constituting R²and R⁴ can be appropriately selected depending on the performance andthe like required for the lubricant containing a fluorine-containingether compound.

Examples of polar groups of divalent linking groups having a polar grouprepresented by R² and R⁴ include a hydroxyl group (—OH), an amino group(—NH₂), a carboxyl group (—COOH), an aldehyde group (—COH), a carbonylgroup (—CO—), and a sulfonic acid group (—SO₃H). Among these,particularly, the polar group is preferably a hydroxyl group. Thehydroxyl group has a large interaction with the protective layer,particularly the protective layer formed of a carbon-based material.Therefore, when the polar group of R² and/or R⁴ is a hydroxyl group, thelubricating layer containing the fluorine-containing ether compound hashigh adhesiveness (adhesion) to the protective layer.

When the polar group of R² and/or R⁴ contains a hydroxyl group, thetotal number of a hydroxyl group contained in R² and a hydroxyl groupcontained in R⁴ in Formula (1) is preferably 2 to 6, more preferably 2to 5, and still more preferably 3 to 4. When the total number of thehydroxyl groups is 2 or more, the interaction between the hydroxylgroups of R² and R⁴ and the protective layer can be obtained moreeffectively. As a result, a fluorine-containing ether compound which canform a lubricating layer having a higher adhesiveness (adhesion) to theprotective layer is obtained. In addition, when the total number of thehydroxyl groups is 6 or less, it is possible to reduce the occurrence ofpickup, because it is possible to prevent polar groups which are notinvolved in bonding between the lubricating layer and the active siteson the protective layer from attracting environmental substances, whichproduce contamination substances, to the lubricating layer.

It is preferable for R² and/or R⁴ to contain 1 to 3 linking groupsrepresented by the following Formula (2), and it is more preferable thatboth R² and R⁴ contain 1 to 3 linking groups represented by thefollowing Formula (2):

—CH₂CH(OH)CH₂—  (2)

The linking group represented by Formula (2) is a linking group having ahydroxyl group, which is a group having a particularly large interactionwith the protective layer among polar groups. In addition, in thelinking group represented by Formula (2), a methylene group (—CH₂—) isdisposed on both sides of the carbon atom to which the hydroxyl group isbonded. Therefore, when R² and/or R⁴ contains 1 to 3 linking groupsrepresented by Formula (2), for the following reasons, afluorine-containing ether compound which can form a lubricating layerwith higher adhesiveness (adhesion) to the protective layer is obtained.

That is, at least the methylene group and the oxygen atom (—O—) of R² orR⁴ are disposed between the carbon atom to which the hydroxyl group ofthe linking group represented by Formula (2) is bonded and R¹ or R⁵.Therefore, the distance between the hydroxyl group contained in thelinking group represented by Formula (2) and any one selected from thegroup consisting of an alkenyl group having 2 to 8 carbon atoms, analkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup of R¹ and/or R⁵ is appropriate. Therefore, the hydroxyl group ofthe linking group represented by Formula (2) and the terminal grouprepresented by R¹ and/or R⁵ each independently exhibit a favorableinteraction with the protective layer, and each is independently likelyto be bonded to a plurality of functional groups (active sites) presenton the protective layer.

In addition, in the linking group represented by Formula (2), since amethylene group is disposed on both sides of the carbon atom to whichthe hydroxyl group is bonded, when R² and/or R⁴ contains 2 to 3 linkinggroups represented by Formula (2), the distance between the hydroxylgroups contained in the linking groups represented by Formula (2) isappropriate. As a result, even if the number of hydroxyl groupscontained in the linking groups represented by Formula (2) is plural,the hydroxyl groups contained in the linking groups represented byFormula (2) are likely to be involved in binding to the active sites onthe protective layer.

In addition, when R² and/or R⁴ contains 1 to 3 linking groupsrepresented by Formula (2), R² and/or R⁴ contains 1 to 3 hydroxylgroups. Therefore, the number of hydroxyl groups contained in R² and/orR⁴ tends to be appropriate, and it is possible to prevent the polarityof the fluorine-containing ether compound from becoming too high and toprevent pickup from occurring.

The number of linking groups represented by Formula (2) is preferablyadjusted so that the total number of a hydroxyl group contained in R²and a hydroxyl group contained in R⁴ in Formula (1) becomes 2 to 5, andis more preferably adjusted so that the total number becomes 3 to 4,since a fluorine-containing ether compound which can form a lubricatinglayer with better adhesion to the protective layer is obtained.

R² and/or R⁴ is preferably a linking group represented by the followingFormula (2-1), and more preferably, both R² and R⁴ are linking groupsrepresented by the following Formula (2-1). In Formula (2-1), the oxygenatom on the left side is an oxygen atom bonded to R¹ or R⁵.

—O—X—(Y¹X)_(a)—Y²—  (2-1)

(in Formula (2-1), a represents an integer of 0 to 2; X representsFormula (2); Y¹ represents any one selected from the group consisting of—O—, —CH₂—, —CH₂O—, and —OCH₂—; and Y² represents —O— or —CH₂O—).

R² and/or R⁴ is preferably a linking group represented by Formula (2-1)so that the fluorine-containing ether compound is easily synthesized.

In the linking group represented by Formula (2-1), in Formula (2-1), arepresents an integer of 0 to 2. Since a in the linking grouprepresented by Formula (2-1) is 0 or more, when R² and/or R⁴ is alinking group represented by Formula (2-1), 1 or more hydroxyl groups,which have a particularly large interaction with the protective layer,are contained as polar groups. As a result, a fluorine-containing ethercompound which can form a lubricating layer with better adhesion to theprotective layer is obtained. In addition, in the linking grouprepresented by Formula (2-1), since a in Formula (2-1) is 2 or less, itis possible to prevent the occurrence of pickup, in which the polarityof the fluorine-containing ether compound becomes too high due to alarge number of hydroxyl groups in the linking group represented byFormula (2-1), and the lubricant containing the compound adheres asforeign matter (smear).

In addition, in the linking group represented by Formula (2-1), when ain Formula (2-1) is 1 or 2, the distance between the hydroxyl groupscontained in the linking group represented by Formula (2-1) isappropriate. As a result, even if the number of hydroxyl groupscontained in R² and/or R⁴ is plural, the hydroxyl groups contained in R²and/or R⁴ are likely to be involved in binding to the active sites onthe protective layer.

In the linking group represented by Formula (2-1), X in Formula (2-1) isFormula (2), Y¹ represents any one selected from the group consisting of—O—, —CH₂—, —CH₂O—, and —OCH₂—, and Y² represents —O— or —CH₂O—. Y¹ andY² may be the same as or different from each other.

When R² and/or R⁴ is a linking group represented by Formula (2-1). R²and R¹, and/or R¹ and R⁵ are bonded by an ether bond, and an ether bondis provided between R² and R³ and/or between R⁴ and R³. As a result, afluorine-containing ether compound having appropriate flexibility isobtained, and a lubricating layer having better chemical substanceresistance and wear resistance can be formed.

In the linking group represented by Formula (2-1). Y¹ is preferably anether bond (—O—) or a group containing an ether bond, and morepreferably, Y¹ and Y² are —O—. In this case, compared with when Y¹ isCH₂, a fluorine-containing ether compound having appropriate flexibilityis obtained. Therefore, the interaction between the hydroxyl groupcontained in the linking group represented by Formula (2-1) and theprotective layer becomes strong.

In the fluorine-containing ether compound represented by Formula (1). R²and R⁴ may be the same as or different from each other.

(Terminal groups represented by R¹ and R⁵)

In the fluorine-containing ether compound represented by Formula (1). R¹and R⁵ are terminal groups bonded to the oxygen atom of R² or R⁴, andmay be the same as or different from each other. At least one ofterminal groups represented by R¹ and R⁵ is any one selected from thegroup consisting of an alkenyl group having 2 to 8 carbon atoms, analkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup.

In the fluorine-containing ether compound represented by Formula (1),the π bond of the unsaturated bond of the terminal group composed of anyone selected from the group consisting of an alkenyl group having 2 to 8carbon atoms, an alkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup exhibits an appropriate interaction with the protective layer.Therefore, the terminal group has a function of improving the adhesionbetween the lubricating layer and the protective layer and forming alubricating layer having favorable chemical substance resistance andwear resistance.

In particular, the terminal group composed of an aromaticheterocycle-containing group is strongly adsorbed, since the π bond ofthe unsaturated bond and the heteroatom of the aromatic heterocycle forman interaction with the protective layer. Therefore, a lubricating layerhaving better chemical substance resistance and wear resistance can beformed.

In the fluorine-containing ether compound represented by Formula (1),the type of an alkenyl group having 2 to 8 carbon atoms, an alkynylgroup having 3 to 8 carbon atoms, an aromatic hydrocarbon-containinggroup, and an aromatic heterocycle-containing group constituting R¹and/or R⁵ can be appropriately selected depending on the performance andthe like required for the lubricant containing a fluorine-containingether compound.

Since the alkenyl group as the terminal group represented by R¹ and/orR⁵ has 2 to 8 carbon atoms, the terminal group does not cause sterichindrance. Therefore, a fluorine-containing ether compound in which R¹and/or R⁵ represents an alkenyl group having 2 to 8 carbon atomsexhibits favorable affinity with the protective layer.

The alkenyl group having 2 to 8 carbon atoms is not particularlylimited, and examples thereof include a vinyl group, an allyl group, acrotyl group, a butenyl group, a beta-methallyl group, a methylbutenylgroup, a pentenyl group, a hexenyl group, a heptenyl group, and anoctenyl group. Among these, from the viewpoint of exhibiting favorableaffinity with the protective layer of the magnetic recording medium, avinyl group, an allyl group, a 3-butenyl group, and a 4-pentenyl group,which are alkenyl groups having 2 to 5 carbon atoms, are preferable, andan allyl group is particularly preferable.

When the alkenyl group as the terminal group represented by R¹ and/or R⁵is an alkenyl group having 3 or more carbon atoms, a double bond ispreferably disposed at the terminal of the fluorine-containing ethercompound. In this case, compared with when a double bond is disposed ata position other than the terminal of the fluorine-containing ethercompound, it is easy to obtain an interaction between the alkenyl groupthat is R¹ and/or R⁵ and the protective layer. As a result, the affinitybetween the lubricating layer containing the fluorine-containing ethercompound and the protective layer becomes better.

Since the alkynyl group as the terminal group represented by R¹ and/orR⁵ has 3 to 8 carbon atoms, the terminal group does not cause sterichindrance. Therefore, the fluorine-containing ether compound in which R¹and/or R⁵ represents an alkynyl group having 3 to 8 carbon atomsexhibits favorable affinity with the protective layer.

The alkynyl group having 3 to 8 carbon atoms is not particularlylimited, and examples thereof include a propynyl group, a propargylgroup, a butynyl group, a methylbutynyl group, a pentynyl group, amethylpentynyl group, a hexynyl group, a methylhexynyl group, a heptenylgroup, and an octynyl group. Among these, from the viewpoint ofexhibiting favorable affinity with the protective layer of the magneticrecording medium, a 1-propynyl group, a propargyl group, a butynylgroup, and a pentynyl group, which are alkynyl groups having 3 to 5carbon atoms, are preferable, and a propargyl group is particularlypreferable. In addition, the alkynyl group may have a form in which analkenyl group is contained in the molecule, such as a vinylpentynylgroup.

When the alkynyl group as the terminal group represented by R¹ and/or R⁵is an alkynyl group having 3 or more carbon atoms, a triple bond ispreferably disposed at the terminal of the fluorine-containing ethercompound. In this case, compared with when a triple bond is disposed ata position other than the terminal of the fluorine-containing ethercompound, it is easy to obtain an interaction between the alkynyl groupthat is R¹ and/or R⁵ and the protective layer. As a result, the affinitybetween the lubricating layer containing the fluorine-containing ethercompound and the protective layer becomes better.

Examples of groups containing an aromatic hydrocarbon as the terminalgroup represented by R¹ and/or R⁵ include a phenyl group, amethoxyphenyl group, a phenylfluoride group, a naphthyl group, aphenethyl group, a methoxyphenethyl group, a phenethylfluoride group, abenzyl group, a methoxybenzyl group, a naphthylmethyl group, and amethoxynaphthyl group.

These groups containing an aromatic hydrocarbon may have a substituentsuch as an alkyl group, an alkoxy group, a hydroxyl group, a mercaptogroup, a carboxyl group, a carbonyl group, an amino group, and a cyanogroup. The substituent preferably does not contain hydroxyl groups inorder to prevent the wear resistance of the lubricating layer from beingimpaired due to an excessive number of hydroxyl groups.

Among the groups containing an aromatic hydrocarbon, any one selectedfrom the group consisting of a phenyl group, a methoxyphenyl group, aphenylfluoride group, a phenethyl group, a methoxyphenethyl group, and aphenethylfluoride group is preferable. When R¹ and/or R⁵ is any oneselected from the group consisting of a phenyl group, a methoxyphenylgroup, a phenylfluoride group, a phenethyl group, a methoxyphenethylgroup, and a phenethylfluoride group, a fluorine-containing ethercompound which can form a lubricating layer having high affinity withthe protective layer and having better wear resistance is obtained.

Examples of groups containing an aromatic heterocycle as the terminalgroup represented by R¹ and/or R⁵ include a pyrrolyl group, a pyrazolylgroup, a methylpyrazolylmethyl group, an imidazolyl group, a furylgroup, a furfuryl group, an oxazolyl group, an isooxazolyl group, athienyl group, a thienylethyl group, a methylthiazoleethyl group, athiazolyl group, a methylthiazolylethyl group, an isothiazolyl group, apyridyl group, a pyrimidinyl group, a pyridazinyl group, a pyrazinylgroup, an indolinyl group, a benzofuranyl group, a benzothienyl group, abenzoimidazolyl group, a benzooxazolyl group, a benzothiazolyl group, abenzopyrazolyl group, a benzoisooxazolyl group, a benzoisothiazolylgroup, a quinolyl group, an isoquinolyl group, a quinazolinyl group, aquinoxalinyl group, a phthalazinyl group, and a cinnolinyl group.

These groups containing an aromatic heterocycle may have a substituentsuch as an alkyl group, an alkoxy group, a hydroxyl group, a mercaptogroup, a carboxy group, a carbonyl group, an amino group, and a cyanogroup. The substituent preferably does not contain hydroxyl groups inorder to prevent the wear resistance of the lubricating layer from beingimpaired due to an excessive number of hydroxyl groups.

Among the groups containing an aromatic heterocycle, any one selectedfrom the group consisting of a group containing a thiophene ring, agroup containing a thiazole ring, and a group containing a pyrazole ringis preferable. If R¹ and/or R⁵ is any one selected from the groupconsisting of a group containing a thiophene ring, a group containing athiazole ring, and a group containing a pyrazole ring, afluorine-containing ether compound which can form a lubricating layerhaving high affinity with the protective layer and having better wearresistance is obtained.

In the fluorine-containing ether compound represented by Formula (1),when both the terminal groups represented by R¹ and R⁵ are any oneselected from the group consisting of an alkenyl group having 2 to 8carbon atoms, an alkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup, R¹ and R⁵ may be the same as or different from each other.

When R¹ and R⁵ are the same, this is preferable because the structuresof both terminals are the same and thus the fluorine-containing ethercompound is likely to uniformly wet and spread on the protective layer,and a lubricating layer having uniform coating is easily obtained.

In addition, when both the terminal groups represented by R¹ and R⁵ areany one selected from the group consisting of an alkenyl group having 2to 8 carbon atoms, an alkynyl group having 3 to 8 carbon atoms, anaromatic hydrocarbon-containing group, and an aromaticheterocycle-containing group, and R¹ and R⁵ are different from eachother, one of R¹ and R⁵ is preferably any one selected from the groupconsisting of an allyl group, a 3-butenyl group, and a 4-pentenyl group,because a fluorine-containing ether compound exhibiting favorableaffinity with the protective layer is obtained.

In the fluorine-containing ether compound represented by Formula (1),when only one of the terminal groups represented by R¹ and R⁵ (forexample, R¹) is any one selected from the group consisting of an alkenylgroup having 2 to 8 carbon atoms, an alkynyl group having 3 to 8 carbonatoms, an aromatic hydrocarbon-containing group, and an aromaticheterocycle-containing group, the other terminal group (for example, R⁵)may be any group except an alkenyl group having 2 to 8 carbon atoms, analkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup, and is not particularly limited.

In this case, the other terminal group (for example, R⁵) preferably doesnot contain hydroxyl groups in order to prevent the wear resistance ofthe lubricating layer from being impaired due to an excessive number ofhydroxyl groups.

In the fluorine-containing ether compound represented by Formula (1),when two PFPE chains represented by R³ are the same, R² and R⁴ are thesame, and R¹ and R⁵ are the same, this is preferable because thecompound can be easily and efficiently produced. In addition, since sucha fluorine-containing ether compound has a symmetric structure centeredon a glycerin structure, this is preferable because the compound islikely to uniformly wet and spread on the protective layer, and alubricating layer having uniform coating is easily obtained.

Specifically, the fluorine-containing ether compound represented byFormula (1) is preferably any of the compounds represented by thefollowing Formulae (A) to (P). Here, in Formulae (A) to (P), since ma1to mn1, ma2 to mn2, na1 to nn1, na2 to nn2, po1, po2, qp1, and qp2 arevalues indicating an average degree of polymerization, they are notnecessarily integers.

When the compound represented by Formula (1) is any of the compoundsrepresented by Formulae (A) to (P), this is preferable because a rawmaterial is easily available, and moreover, it is possible to form alubricating layer having excellent adhesion and better chemicalsubstance resistance and wear resistance even if the thickness is thin.

In all of the compounds represented by the following Formulae (A) to(P), two PFPE chains represented by R³ in Formula (1) are the same. Inall of the compounds represented by the following Formulae (A) to (P).R² and R⁴ are a linking group represented by Formula (2-1), and Y² inFormula (2-1) is —O—.

In all of the compounds represented by the following Formulae (A) to(D), R¹ and R⁵ represent an allyl group, and R³ is represented byFormula (3).

In all of the compounds represented by Formulae (A) to (C), a in Formula(2-1) for R² is 0. In the compound represented by Formula (A), a inFormula (2-1) for R¹ is 0, in the compound represented by Formula (B), ain Formula (2-1) for R¹ is 1, and Y¹ represents —O—, and in the compoundrepresented by Formula (C), a in Formula (2-1) for R⁴ is 2, and Y¹represents —O—.

In the compound represented by Formula (D), a in Formula (2-1) for R²and R⁴ is 1, and Y¹ represents —O—.

In the compound represented by the following Formula (E). R¹ and R⁵represent a 3-butenyl group, and R³ is represented by Formula (3). Inthe compound represented by Formula (E), a in Formula (2-1) for R² andR⁴ is 1, and Y¹ represents —OCH₂—.

In the compound represented by the following Formula (F), R¹ and R⁵represent a 4-pentenyl group, and R³ is represented by Formula (3). Inthe compound represented by Formula (F), a in Formula (2-1) for R² andR⁴ is 1, and Y¹ represents —O—.

In the compound represented by the following Formula (G), R¹ and R⁵represent a propargyl group, and R³ is represented by Formula (3). Inthe compound represented by Formula (G), a in Formula (2-1) for R² andR⁴ is 1, and Y¹ represents —O—.

In the compound represented by the following Formula (H), R¹ and R⁵represent a thienylethyl group, and R³ is represented by Formula (3). Inthe compound represented by Formula (H), a in Formula (2-1) for R² andR⁴ is 0.

In the compound represented by the following Formula (1). R¹ and R⁵represent a methylpyrazolylmethyl group, and R³ is represented byFormula (3). In the compound represented by Formula (1), a in Formula(2-1) for R² and R⁴ is 0.

In the compound represented by the following Formula (J). R¹ and R⁵represent a methylthiazoleethyl group, and R³ is represented by Formula(3). In the compound represented by Formula (J), a in Formula (2-1) forR² and R⁴ is 0.

In the compound represented by the following Formula (K). R¹ representsan allyl group. R⁵ represents a 3-butenyl group, and R³ is representedby Formula (3). In the compound represented by Formula (K), a in Formula(2-1) for R² is 1, and Y¹ represents —O—, and a in Formula (2-1) for R⁴is 1, and Y¹ represents-OCH₂—.

In the compound represented by the following Formula (L). R¹ representsan allyl group. R⁵ represents a phenyl group, and R³ is represented byFormula (3). In the compound represented by Formula (L), a in Formula(2-1) for R² is 1, and Y¹ represents —O—, and a in Formula (2-1) for R⁴is 0.

In the compound represented by the following Formula (M). R¹ representsan allyl group. R⁵ represents a thienylethyl group, and R³ isrepresented by Formula (3). In the compound represented by Formula (M),a in Formula (2-1) for R² is 1, and Y¹ represents —O—, and a in Formula(2-1) for R⁴ is 0.

In the compound represented by the following Formula (N). R¹ representsa phenyl group. R⁵ represents a thienylethyl group, and R¹ isrepresented by Formula (3). In the compound represented by Formula (N),a in Formula (2-1) for R² and R⁴ is 0.

In the compounds represented by the following Formulae (O) and (P). R¹and R⁵ both are allyl groups, and a in Formula (2-1) for R² and R⁴ is 1,and Y¹ represents —O—. In the compound represented by Formula (O). R¹ isrepresented by Formula (4). In the compound represented by Formula (P).R³ is represented by Formula (5).

(in Formula (A), ma1, ma2, na1, and na2 indicate an average degree ofpolymerization, ma1 and ma2 represent 1 to 20, and na1 and na2 represent0 to 20).

(in Formula (B), mb1, mb2, nb1, and nb2 indicate an average degree ofpolymerization, mb1 and mb2 represent 1 to 20, and nb1 and nb2 represent0 to 20).

(in Formula (C), mc1, mc2, nc1, and nc2 indicate an average degree ofpolymerization, mc1 and mc2 represent 1 to 20, and nc1 and nc2 represent0 to 20).

(in Formula (D), md1, md2, nd1, and nd2 indicate an average degree ofpolymerization, md1 and md2 represent 1 to 20, and nd1 and nd2 represent0 to 20).

(in Formula (E), me1, me2, ne1, and ne2 indicate an average degree ofpolymerization, me1 and me2 represent 1 to 20, and ne1 and ne2 represent0 to 20).

(in Formula (F), mf1, mf2, nf1, and nf2 indicate an average degree ofpolymerization, mf1 and mf2 represent 1 to 20, and nf1 and nf2 represent0 to 20).

(in Formula (G), mg1, mg2, ng1, and ng2 indicate an average degree ofpolymerization, mg1 and mg2 represent 1 to 20, and ng1 and ng2 represent0 to 20), and

(in Formula (H), mh1, mh2, nh1, and nh2 indicate an average degree ofpolymerization, mh1 and mh2 represent 1 to 20, and nh1 and nh2 represent0 to 20).

(in Formula (1), mi1, mi2, ni1, and ni2 indicate an average degree ofpolymerization, mi1 and mi2 represent 1 to 20, and ni1 and ni2 represent0 to 20).

(in Formula (J), mj1, mj2, nj1, and nj2 indicate an average degree ofpolymerization, mj1 and mj2 represent 1 to 20, and nj1 and nj2 represent0 to 20).

(in Formula (K), mk1, mk2, nk1, and nk2 indicate an average degree ofpolymerization, mk1 and mk2 represent 1 to 20, and nk1 and nk2 represent0 to 20), and

(in Formula (L), ml1 ml2, nl1, and nl2 indicate an average degree ofpolymerization, ml1 and ml2 represent 1 to 20, and nl1 and nl2 represent0 to 20).

(in Formula (M), mm1, mm2, nm1, and nm2 indicate an average degree ofpolymerization, mm1 and mm2 represent 1 to 20, and nm1 and nm2 represent0 to 20).

(in Formula (N), mn1, mn2, nn1, and nn2 indicate an average degree ofpolymerization, mn1 and mn2 represent 1 to 20, and nn1 and nn2 represent0 to 20).

(in Formula (O), po1 and po2 indicate an average degree ofpolymerization, and each represent 1 to 20), and

(in Formula (P), qp1 and qp2 indicate an average degree ofpolymerization, and each represent 1 to 10).

In Formulae (A) to (P), ma1 to mn1, ma2 to mn2, na1 to nn1, na2 to nn2,po1, po2, qp1, and qp2 may each have a range arbitrarily selected fromthe ranges described above. For example, ma1 to nn1, ma2 to mn2, po1,and po2 may be 1 to 15, 1 to 10, 1 to 8, 1 to 5, 2 to 3, or the like,na1 to nn1, and na2 to nn2 may be 0 to 15, 0 to 10.0 to 8.0 to 5, 1 to6, 2 to 3, or the like, qp1 and qp2 may be 1 to 8, 1 to 5, 2 to 3, orthe like.

The number-average molecular weight (Mn) of the fluorine-containingether compound of the present embodiment is preferably in a range of 500to 10,000, and particularly preferably in a range of 1,000 to 5,000. Ifthe number-average molecular weight is 500 or more, the lubricatinglayer composed of the lubricant containing the fluorine-containing ethercompound of the present embodiment has excellent heat resistance. Thenumber-average molecular weight of the fluorine-containing ethercompound is more preferably 1,000 or more. In addition, when thenumber-average molecular weight is 10,000 or less, the viscosity of thefluorine-containing ether compound becomes appropriate, and when alubricant containing the compound is applied, a lubricating layer havinga thin film thickness can be easily formed. The number-average molecularweight of the fluorine-containing ether compound is preferably 5,000 orless so that the compound has a viscosity at which handling is easy whenapplied to a lubricant.

The number-average molecular weight (Mn) of the fluorine-containingether compound are values measured by ¹H-NMR and ¹⁹F-NMR, specifically,by ¹H-NMR and ¹⁹F-NMR using AVANCE111400 (commercially available fromBruker BioSpin). More specifically, the number of repeating units of thePFPE chain is calculated from the integrated value measured by ¹⁹F-NMRto obtain a number-average molecular weight. In the measurement ofnuclear magnetic resonance (NMR), a sample is diluted with ahexafluorobenzene/d-acetone (4/1v/v) solvent, and measurement isperformed. The standard for ¹⁹F-NMR chemical shift is −164.7 ppm for thepeak of hexafluorobenzene, and the standard for ¹H-NMR chemical shift is2.2 ppm for the peak of acetone.

The fluorine-containing ether compound of the present embodimentpreferably has a molecular weight dispersity (ratio of weight-averagemolecular weight (Mw)/number-average molecular weight (Mn)) of 1.3 orless, by performing molecular weight fractionation by an appropriatemethod.

In the present embodiment, the method for molecular weight fractionationis not particularly limited, and for example, molecular weightfractionation using a silica gel column chromatography method, a gelpermeation chromatography (GPC) method or the like, molecular weightfractionation using a supercritical extraction method, or the like canbe used.

“Production Method”

A method of producing a fluorine-containing ether compound of thepresent embodiment is not particularly limited, and a conventionallyknown production method can be used for production. Thefluorine-containing ether compound of the present embodiment can beproduced using, for example, the following production method.

(When two PFPE chains represented by R³ are the same, and R¹—R²— andR⁵—R⁴— are the same)

When a compound in which, in Formula (1) two PFPE chains represented byR³ are the same, and R¹—R²— and R⁵—R⁴— are the same (that is, R¹ and R⁵are the same and R² and R⁴ are the same) is produced, first, afluorine-based compound in which a hydroxymethyl group (—CH₂OH) isdisposed at both terminals of the perfluoropolyether chain correspondingto R³ in Formula (1) is prepared.

Next, the hydroxyl group of the hydroxymethyl group disposed at oneterminal of the fluorine-based compound and the epoxy group of an epoxycompound having a group that forms R¹—R²— (=group that forms R⁵—R⁴—) inFormula (1) are reacted. Accordingly, an intermediate compound having agroup corresponding to R¹—R²— at one terminal of the perfluoropolyetherchain corresponding to R¹ is obtained.

Regarding the epoxy compound having a group that forms R¹—R²— (=groupthat forms R⁵—R⁴—) in Formula (1), for example, the compoundsrepresented by the following Formulae (6a) to (6c), (7a) to (7b-2),(8a), (8b), (9a), (9b), (10a), (11a), and (12a) can be used.

When the fluorine-based compound is reacted with the epoxy compound tosynthesize the intermediate compound, the hydroxyl group of the epoxycompound may be protected using an appropriate protecting group, andthen reacted with the fluorine-based compound.

The epoxy compound having a group that forms R¹—R²— (=group that formsR⁵—R⁴—) in Formula (1) can be produced, for example, as shown in thefollowing Formula (13), using a method of reacting an alcohol having astructure corresponding to the terminal group represented by R¹ or R⁵ inFormula (1) with epibromohydrin.

In addition, the epoxy compound may be produced, for example, as shownin the following Formula (14), using a method in which an alcohol havinga structure corresponding to the terminal group represented by R¹ or R⁵in Formula (1) and allyl glycidyl ether are subjected to an additionreaction, and the compound obtained by the addition reaction is thenoxidized.

In addition, the epoxy compound may be produced, for example, as shownin the following Formula (05), using a method in which an alcohol havinga structure corresponding to the terminal group represented by R¹ or R⁵in Formula (1) is reacted with glycerin diglycidyl ether.

For the epoxy compound, a commercial product may be purchased and used.

Then, the intermediate compound having a group corresponding to R¹—R²—at one terminal of the perfluoropolyether chain corresponding to R¹ isreacted with epibromohydrin.

By performing the above processes, a compound in which a glycerinstructure is provided in the center of the chain structure, and inFormula (1), two PFPE chains represented by R¹ are the same, and R¹—R²—and R⁵—R⁴— are the same is obtained.

(When any one or more of R¹ and R⁵, R² and R⁴, and two PFPE chainsrepresented by R³ are different from each other)

In this case also, in the same manner as in the case of producing acompound in which, in Formula (1), two PFPE chains represented by R³ arethe same, and R¹—R²— and R⁵—R⁴— are the same, an intermediate compoundhaving a group corresponding to R¹—R²— at one terminal of theperfluoropolyether chain corresponding to R³ is produced.

Next, the intermediate compound having a group corresponding to R¹—R²—at one terminal is reacted with epibromohydrin to produce a firstintermediate compound having a group corresponding to R¹—R²— at oneterminal of the perfluoropolyether chain corresponding to R³ and anepoxy group at the other terminal.

Next, in the same manner as the intermediate compound having a groupcorresponding to R¹—R²— at one terminal, a second intermediate compoundhaving a group corresponding to R⁵—R⁴— at one terminal of theperfluoropolyether chain corresponding to R³ is produced.

Then, the first intermediate compound is reacted with the secondintermediate compound.

By performing the above processes, a compound in which a glycerinstructure is provided in the center of the chain structure, and inFormula (1), any one or more of R¹ and R⁵, R² and R⁴, and two PFPEchains represented by R³ are different from each other can be produced.

The fluorine-containing ether compound of the present embodiment is acompound represented by Formula (1) in which a glycerin structure isdisposed in the center of the chain structure, a PFPE chain representedby R³, a methylene group, divalent linking groups having a polar grouprepresented by R² and R⁴, and terminal groups represented by R¹ and R⁵are bonded in that order to both sides via a methylene group (—CH₂—),and at least one terminal group of R¹ and R⁵ is any one selected fromthe group consisting of an alkenyl group having 2 to 8 carbon atoms, analkynyl group having 3 to 8 carbon atoms, an aromatichydrocarbon-containing group, and an aromatic heterocycle-containinggroup. Therefore, the lubricating layer formed on the protective layerusing the lubricant containing the fluorine-containing ether compound ofthe present embodiment has excellent adhesion to the protective layereven if the thickness is thin, and has favorable chemical substanceresistance and wear resistance.

[Lubricant for Magnetic Recording Medium]

A lubricant for a magnetic recording medium of the present embodimentcontains the fluorine-containing ether compound represented by Formula(1).

The lubricant of the present embodiment can be used by being mixed witha known material used as a material for a lubricant as necessary as longas the characteristics of the fluorine-containing ether compoundrepresented by Formula (1) are not impaired due to the inclusion of theknown material.

Specific examples of known materials include, for example, FOMBLIN(registered trademark) ZDIAC. FOMBLIN ZDEAL, and FOMBLIN AM-2001 (allcommercially available from Solvay Solexis), and Moresco A20H(commercially available from Moresco). A known material used incombination with the lubricant of the present embodiment preferably hasa number-average molecular weight of 1,000 to 10,000.

When the lubricant of the present embodiment contains a material otherthan the fluorine-containing ether compound represented by Formula (1),the content of the fluorine-containing ether compound represented byFormula (1) in the lubricant of the present embodiment is preferably 50mass % or more, more preferably 60 mass % or more, and still morepreferably 70 mass % or more. The upper limit thereof can be arbitrarilyselected, and may be, for example, 99 mass % or less, 95 mass % or less,90 mass % or less, or 80 mass % or less.

Since the lubricant of the present embodiment contains thefluorine-containing ether compound represented by Formula (1), it cancover the surface of the protective layer with high coverage even if thefilm thickness is thin, and form a lubricating layer having excellentchemical substance resistance and wear resistance.

[Magnetic Recording Medium]

In a magnetic recording medium of the present embodiment, at least amagnetic layer, a protective layer, and a lubricating layer aresequentially provided on a substrate.

In the magnetic recording medium of the present embodiment, asnecessary, one, two or more underlayers can be provided between thesubstrate and the magnetic layer. In addition, at least one of theadhesive layer and the soft magnetic layer can be provided between theunderlayer and the substrate.

FIG. 1 is a schematic cross-sectional view showing a magnetic recordingmedium according to one embodiment of the present invention.

A magnetic recording medium 10 of the present embodiment has a structurein which an adhesive layer 12, a soft magnetic layer 13, a firstunderlayer 14, a second underlayer 15, a magnetic layer 16, a protectivelayer 17, and a lubricating layer 18 are sequentially provided on asubstrate 11.

“Substrate”

As the substrate 11, for example, a non-magnetic substrate in which afilm made of NiP or a NiP alloy is formed on a base made of a metal oran alloy material such as Al or an Al alloy can be used.

In addition, as the substrate 11, a non-magnetic substrate made of anon-metal material such as glass, a ceramic, silicon, silicon carbide,carbon, and a resin may be used, or a non-magnetic substrate in which afilm of NiP or a NiP alloy is formed on a base made of these non-metalmaterials may be used.

Since the glass substrate has rigidity and excellent smoothness, it issuitable for increasing the recording density. Examples of glasssubstrates include an aluminosilicate glass substrate, and a chemicallyreinforced aluminosilicate glass substrate is particularly suitable.

The roughness of the main surface of the substrate 11 is preferablyultra-smooth with an Rmax of 6 nm or less and an Ra of 0.6 nm or less.Here, the surface roughnesses Rmax and Ra herein are based on theprovisions of JIS B0601.

“Adhesive Layer”

The adhesive layer 12 prevents the progress of corrosion of thesubstrate 11 that occurs when the substrate 11 and the soft magneticlayer 13 provided on the adhesive layer 12 are disposed in contact witheach other.

The material of the adhesive layer 12 can be appropriately selected fromamong, for example, Cr, a Cr alloy, Ti, a Ti alloy, CrTi, NiAl, and anAlRu alloy. The adhesive layer 12 can be formed by, for example, asputtering method.

“Soft Magnetic Layer”

The soft magnetic layer 13 preferably has a structure in which a firstsoft magnetic film, an intermediate layer made of a Ru film, and asecond soft magnetic film are sequentially laminated. That is, the softmagnetic layer 13 preferably has a structure in which an intermediatelayer made of a Ru film is interposed between two soft magnetic filmlayers, and thus the soft magnetic films above and below theintermediate layer are bonded by anti-ferromagnetic coupling (AFC).

Examples of materials of the first soft magnetic film and the secondsoft magnetic film include a CoZrTa alloy and a CoFc alloy.

It is preferable to add any of Zr, Ta, and Nb to the CoFe alloy used forthe first soft magnetic film and the second soft magnetic film. Thereby,the amorphization of the first soft magnetic film and the second softmagnetic film can be promoted, the orientation of the first underlayer(seed layer) can be improved, and the floating height of the magnetichead can be reduced.

The soft magnetic layer 13 can be formed by, for example, a sputteringmethod.

“First Underlayer”

The first underlayer 14 is a layer that controls the orientation and thecrystal size of the second underlayer 15 and the magnetic layer 16provided thereon.

Examples of the first underlayer 14 include a Cr layer, a Ta layer, a Rulayer, a CrMo alloy layer, a CoW alloy layer, a CrW alloy layer, a CrValloy layer, and a CrTi alloy layer.

The first underlayer 14 can be formed by, for example, a sputteringmethod.

“Second Underlayer”

The second underlayer 15 is a layer that controls the orientation of themagnetic layer 16 such that it becomes favorable. The second underlayer15 is preferably a layer made of Ru or a Ru alloy.

The second underlayer 15 may be a single layer or may be composed of aplurality of layers. When the second underlayer 15 is composed of aplurality of layer, all of the layers may be composed of the samematerial, or at least one layer may be composed of a different material.

The second underlayer 15 can be formed by, for example, a sputteringmethod.

“Magnetic Layer”

The magnetic layer 16 is made of a magnetic film in which the axis ofeasy magnetization is in a direction perpendicular or horizontal to thesurface of the substrate. The magnetic layer 16 is a layer containing Coand Pt. or may be a layer furthermore containing an oxide, Cr, B, Cu,Ta, Zr or the like in order to further improve SNR characteristics.

Examples of oxides contained in the magnetic layer 16 include SiO₂, SiO,Cr₂O₃, CoO, Ta₂O₃, and TiO₂.

The magnetic layer 16 may be composed of a single layer or may becomposed of a plurality of magnetic layers made of materials withdifferent compositions.

For example, when the magnetic layer 16 is composed of three layersincluding a first magnetic layer, a second magnetic layer, and a thirdmagnetic layer sequentially laminated from below, the first magneticlayer preferably has a granular structure made of a material containingCo, Cr, and Pt, and further containing an oxide. As the oxide containedin the first magnetic layer, for example, it is preferable to use anoxide of Cr, Si, Ta, Al, Ti, Mg, Co or the like. Among these,particularly, TiO₂, Cr₂O₃, SiO₂ or the like can be preferably used. Inaddition, the first magnetic layer is preferably made of a compositeoxide in which two or more oxides are added. Among these, particularly,Cr₂O₃—SiO₂, Cr₂O₃—TiO₂, SiO₂—TiO₂ or the like can be preferably used.

The first magnetic layer can contain at least one element selected fromthe group consisting of B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru and Re inaddition to Co, Cr, Pt, and an oxide.

For the second magnetic layer, the same material as for the firstmagnetic layer can be used. The second magnetic layer preferably has agranular structure.

The third magnetic layer preferably has a non-granular structure made ofa material containing Co, Cr, and Pt, and not containing an oxide. Thethird magnetic layer can contain at least one element selected from thegroup consisting of B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, Re and Mn inaddition to Co, Cr, and Pt.

When the magnetic layer 16 is formed of a plurality of magnetic layers,it is preferable to provide a non-magnetic layer between adjacentmagnetic layers. When the magnetic layer 16 is composed of three layersincluding a first magnetic layer, a second magnetic layer, and a thirdmagnetic layer, it is preferable to provide a non-magnetic layer betweenthe first magnetic layer and the second magnetic layer, and between thesecond magnetic layer and the third magnetic layer.

For the non-magnetic layer provided between adjacent magnetic layers ofthe magnetic layer 16, for example, Ru, a Ru alloy, a CoCr alloy, aCoCrX1 alloy (X1 represents at least one element selected from the groupconsisting of Pt, Ta, Zr, Re, Ru, Cu, Nb, Ni, Mn, Ge, Si, O, N, W, Mo,Ti, V, Zr and B) or the like can be preferably used.

For the non-magnetic layer provided between adjacent magnetic layers ofthe magnetic layer 16, it is preferable to use an alloy materialcontaining an oxide, a metal nitride, or a metal carbide. Specifically,as the oxide, for example. SiO₂, Al₂O₃, Ta₂O₃, Cr₂O₃, MgO, Y₂O₃, TiO₂ orthe like can be used. As the metal nitride, for example, AlN, Si₃N₄,TaN, CrN or the like can be used. As the metal carbide, for example,TaC, BC, SiC or the like can be used.

The non-magnetic layer can be formed by, for example, a sputteringmethod.

The magnetic layer 16 is preferably a magnetic layer for perpendicularmagnetic recording in which the axis of easy magnetization is in adirection perpendicular to the surface of the substrate in order torealize a higher recording density. The magnetic layer 16 may be amagnetic layer for in-plane magnetic recording.

The magnetic layer 16 may be formed by any conventionally known methodsuch as a deposition method, an ion beam sputtering method, and amagnetron sputtering method. The magnetic layer 16 is generally formedby a sputtering method.

“Protective layer”

The protective layer 17 protects the magnetic layer 16. The protectivelayer 17 may be composed of one layer or may be composed of a pluralityof layers. As the protective layer 17, a carbon-based protective layercan be preferably used, and an amorphous carbon protective layer isparticularly preferable. When the protective layer 17 is a carbon-basedprotective layer, this is preferable because the interaction with thepolar group (particularly the hydroxyl group) contained in thefluorine-containing ether compound in the lubricating layer 18 isfurther improved.

The adhesive force between the carbon-based protective layer and thelubricating layer 18 can be controlled by forming the carbon-basedprotective layer with hydrogenated carbon and/or nitrogenated carbon andadjusting the hydrogen content and/or the nitrogen content in thecarbon-based protective layer. The hydrogen content in the carbon-basedprotective layer measured by a hydrogen forward scattering method (HFS)is preferably 3 atomic % to 20 atomic %. In addition, the nitrogencontent in the carbon-based protective layer measured through X-rayphotoelectron spectroscopy (XPS) is preferably 4 atomic % to 15 atomic%.

Hydrogen and/or nitrogen contained in the carbon-based protective layerneed not be uniformly contained throughout the entire carbon-basedprotective layer. For example, the carbon-based protective layer ispreferably formed as a composition gradient layer in which nitrogen iscontained in the protective layer 17 on the side of the lubricatinglayer 18 and hydrogen is contained in the protective layer 17 on theside of the magnetic layer 16. In this case, the adhesive force betweenthe magnetic layer 16 and the lubricating layer 18, and the carbon-basedprotective layer is further improved.

The film thickness of the protective layer 17 is preferably 1 nm to 7nm. When the film thickness of the protective layer 17 is 1 nm or more,the performance of the protective layer 17 can be sufficiently obtained.The film thickness of the protective layer 17 is preferably 7 nm or lessin order to reduce the thickness of the protective layer 17.

As a film forming method for the protective layer 17, a sputteringmethod using a target material containing carbon, a chemical vapordeposition (CVD) method using a hydrocarbon raw material such asethylene or toluene, an ion beam deposition (IBD) method or the like canbe used.

When a carbon-based protective layer is formed as the protective layer17, for example, a film can be formed by a DC magnetron sputteringmethod. In particular, when a carbon-based protective layer is formed asthe protective layer 17, it is preferable to form an amorphous carbonprotective layer by a plasma CVD method. The amorphous carbon protectivelayer formed by the plasma CVD method has a uniform surface and lowroughness.

“Lubricating Layer”

The lubricating layer 18 prevents contamination of the magneticrecording medium 10. In addition, the lubricating layer 18 reduces africtional force of a magnetic head of a magnetic recording/reproducingdevice, which slides on the magnetic recording medium 10, and improvesthe durability of the magnetic recording medium 10.

As shown in FIG. 1 , the lubricating layer 18 is formed on and incontact with the protective layer 17. The lubricating layer 18 is formedby applying the lubricant for a magnetic recording medium of theembodiment described above to the protective layer 17. Therefore, thelubricating layer 18 contains the above fluorine-containing ethercompound.

When the protective layer 17 disposed below the lubricating layer 18 isa carbon-based protective layer, the lubricating layer 18 is bonded tothe protective layer 17 with a particularly high bonding force. As aresult, even if the thickness of the lubricating layer 18 is thin, it iseasy to obtain the magnetic recording medium 10 in which the surface ofthe protective layer 17 is covered with high coverage, and it ispossible to effectively prevent contamination of the surface of themagnetic recording medium 10.

The average film thickness of the lubricating layer 18 is preferably 0.5nm (5 Å) to 2.0 nm (20 Å), and more preferably 0.5 nm (5 Å) to 1.2 nm(12 Å). When the average film thickness of the lubricating layer 18 is0.5 nm or more, the lubricating layer 18 is formed with a uniform filmthickness without forming an island shape or a mesh shape. Therefore,the lubricating layer 18 can cover the surface of the protective layer17 with high coverage. In addition, when the average film thickness ofthe lubricating layer 18 is 2.0 nm or less, the lubricating layer 18 canbe sufficiently thinned, and the floating height of the magnetic headcan be sufficiently reduced.

“Method of Forming Lubricating Layer”

In order to form the lubricating layer 18, for example, a method inwhich a magnetic recording medium during production in which respectivelayers up to the protective layer 17 are formed on the substrate 11 isprepared, and a solution for forming a lubricating layer is applied ontothe protective layer 17, may be used.

The solution for forming a lubricating layer can be obtained bydispersing and dissolving the lubricant for a magnetic recording mediumof the embodiment described above in a solvent as necessary, andadjusting the viscosity and concentration thereof to be suitable forapplication methods.

Examples of solvents used for the solution for forming a lubricatinglayer include fluorine-based solvents such as Vertrel (registeredtrademark) XF (product name, commercially available from Du Pont-MitsuiFluorochemicals Co., Ltd.).

The method of applying the solution for forming a lubricating layer isnot particularly limited, and examples thereof include a spin coatingmethod, a spraying method, a paper coating method, and a dipping method.

When the dipping method is used, for example, the following method canbe used. First, the substrate 11 in which respective layers up to theprotective layer 17 are formed is immersed in the solution for forming alubricating layer contained in an immersion vessel of a dip coatingdevice. Next, the substrate 11 is lifted from the immersion vessel at apredetermined speed. Accordingly, the solution for forming a lubricatinglayer is applied to the surface of the protective layer 17 of thesubstrate 11.

When the dipping method is used, the solution for forming a lubricatinglayer can be uniformly applied to the surface of the protective layer17, and the lubricating layer 18 with a uniform film thickness can beformed on the protective layer 17.

In the present embodiment, it is preferable to heat the substrate 11 onwhich the lubricating layer 18 is formed. When the heat treatment isperformed, the adhesion between the lubricating layer 18 and theprotective layer 17 is improved, and the adhesive force between thelubricating layer 18 and the protective layer 17 is improved. The heattreatment temperature is preferably 100° C. to 180° C., and morepreferably 100° C. to 160° C. When the heat treatment temperature is100° C. or higher, an effect of improving the adhesion between thelubricating layer 18 and the protective layer 17 is sufficientlyobtained. In addition, when the heat treatment temperature is 180° C. orlower, it is possible to prevent the thermal decomposition of thelubricating layer 18. The heat treatment time can be appropriatelyadjusted according to the heat treatment temperature, and is preferably10 minutes to 120 minutes.

In the present embodiment, in order to further improve the adhesiveforce of the lubricating layer 18 with respect to the protective layer17, an ultraviolet ray (UV) irradiating treatment may be performed onthe lubricating layer 18 before the heat treatment or after the heattreatment.

In the magnetic recording medium 10 of the present embodiment, at leastthe magnetic layer 16, the protective layer 17, and the lubricatinglayer 18 are sequentially provided on the substrate 11. In the magneticrecording medium 10 of the present embodiment, the lubricating layer 18containing the above fluorine-containing ether compound is formed on andin contact with the protective layer 17. The lubricating layer 18 hasexcellent adhesion and favorable chemical substance resistance and wearresistance even if the film thickness is thin. Therefore, the magneticrecording medium 10 of the present embodiment has excellent reliability,and particularly has an excellent silicon contamination minimizationability and durability. Therefore, the magnetic recording medium 10 ofthe present embodiment has a low floating height of the magnetic head(for example, 10 nm or less), and operates stably for a long period oftime even in a harsh environment due to diversity of applications.Therefore, the magnetic recording medium 10 of the present embodiment isparticularly preferable as a magnetic disk mounted in a load unload(LUL) type magnetic disk device.

EXAMPLES

Hereinafter, the present invention will be described in more detail withreference to examples and comparative examples. Here, the presentinvention is not limited only to the following examples.

Example 1

The compound represented by Formula (A) was obtained by the followingmethod.

20 g of a compound (a number-average molecular weight of 1,000 and amolecular weight distribution of 1.1) represented byHOCH₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CH₂OH (in the formula, m whichindicates an average degree of polymerization is 4.5, and n whichindicates an average degree of polymerization is 4.5), 2.28 g of allylglycidyl ether represented by Formula (6a), and 20 mL of t-butanol wereput into a 100 mL eggplant flask under a nitrogen gas atmosphere, andstirred at room temperature until the composition became uniform toprepare a mixture. 0.90 g of potassium tert-butoxide was added to themixture, and the mixture was stirred and reacted at 70° C., for 16hours.

The reaction product obtained after the reaction was cooled to 25° C.transferred to a separatory funnel containing 100 mL of water, andextracted three times with 100 mL of ethyl acetate. The organic layerwas washed with water and dehydrated with anhydrous sodium sulfate.After the drying agent was filtered off, the filtrate was concentrated,and the residue was purified by silica gel column chromatography toobtain 8.84 g of a compound represented by the following Formula (16) asan intermediate.

(in Formula (16), m which indicates an average degree of polymerizationis 4.5, and n which indicates an average degree of polymerization is4.5).

Next, 5.00 g of the compound represented by Formula (16), which was theintermediate obtained above. 0.31 g of epibromohydrin, and 10 mL oft-butanol were put into a 100 mL eggplant flask under a nitrogen gasatmosphere, and stirred at room temperature until the composition becameuniform. 0.60 g of potassium ten-butoxide was added to the uniformliquid, and the mixture was stirred and reacted at 70° C. for 23 hours.

The temperature of the reaction solution obtained after the reaction wasreturned to room temperature, 5 g of a 10% hydrogen chloride/methanolsolution (hydrogen chloride-methanol reagent (5-10%) commerciallyavailable from Tokyo Chemical Industry Co., Ltd.) was added, and themixture was stirred at room temperature for 4 hours. Then, the reactionsolution was transferred to a separatory funnel containing 100 mL ofsaline little by little, and extracted twice with 200 mL of ethylacetate. The organic layer was sequentially washed with 100 mL ofsaline, 100 mL of saturated sodium bicarbonate water, and 100 mL ofsaline, and dehydrated with anhydrous sodium sulfate. After the dryingagent was filtered off, the filtrate was concentrated, and the residuewas purified by silica gel column chromatography to obtain 4.17 g of acompound (A) (in Formula (A), ma1, ma2, na1, and na2 which indicateaverage degrees of polymerization are 4.5).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (A) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.40 to 3.55 (4H), 3.65 to 3.75 (2H), 3.75to 3.85 (4H), 4.00 to 4.15 (17H), 5.10 to 5.15 (2H), 5.25 to 5.30 (2H),5.85 to 5.95 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 2

The compound represented by Formula (B) was obtained by the followingmethod.

The compound represented by Formula (16) was reacted with epibromohydrinto obtain a compound represented by the following Formula (17) as anintermediate.

(in Formula (17), m which indicates an average degree of polymerizationis 4.5, and n which indicates an average degree of polymerization is4.5).

20 g of a compound (a number-average molecular weight of 1,000 and amolecular weight distribution of 1.1) represented byHOCH₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CH₂OH (in the formula, n whichindicates an average degree of polymerization is 4.5, and n whichindicates an average degree of polymerization is 4.5), 5.45 g of acompound represented by the following Formula (6ba), and 20 mL oft-butanol were put into a 100 mL eggplant flask under a nitrogen gasatmosphere, and stirred at room temperature until the composition becameuniform to prepare a mixture. 0.90 g of potassium tert-butoxide wasadded to the mixture, and the mixture was stirred and reacted at 70° C.,for 16 hours.

(in Formula (6ba). THP represents a tetrahydropyranyl group).

Here, the compound represented by Formula (6ba) was synthesized usingthe following method. The secondary hydroxyl group of glycerin diallylether was protected using dihydropyran, and the double bond was oxidizedto obtain an epoxy compound having an allyl group represented by Formula(6ba).

The reaction product obtained after the reaction was cooled to 25° C.transferred to a separatory funnel containing 100 mL of water, andextracted three times with 100 mL of ethyl acetate. The organic layerwas washed with water and dehydrated with anhydrous sodium sulfate.After the drying agent was filtered off, the filtrate was concentrated,and the residue was purified by silica gel column chromatography toobtain 16.5 g of a compound represented by the following Formula (18) asan intermediate.

(in Formula (18), m which indicates the average degree of polymerizationis 4.5, n which indicates the average degree of polymerization is 4.5.THP represents a tetrahydropyranyl group).

Next, 10.0 g of the compound represented by Formula (17), 10.2 g of thecompound represented by Formula (18), and 20 mL of t-butanol were putinto a 100 mL eggplant flask under a nitrogen gas atmosphere, andstirred at rom temperature until the composition became uniform. 0.36 gof potassium tert-butoxide was added to the uniform liquid, and themixture was stirred and reacted at 70° C., for 22 hours.

The temperature of the reaction solution obtained after the reaction wasreturned to room temperature. 20 g of a 10% hydrogen chloride/methanolsolution (hydrogen chloride-methanol reagent (5-10%) commerciallyavailable from Tokyo Chemical Industry Co. Ltd.) was added, and themixture was stirred at room temperature for 4 hours. The reactionsolution was transferred to a separatory funnel containing 100 mL ofsaline little by little, and extracted twice with 200 mL of ethylacetate. The organic layer was sequentially washed with 100 mL ofsaline, 100 mL of saturated sodium bicarbonate water, and 100 mL ofsaline, and dehydrated with anhydrous sodium sulfate. After the dryingagent was filtered off, the filtrate was concentrated, and the residuewas purified by silica gel column chromatography to obtain 14.4 g of acompound (B) (in Formula (B), mb1, mb2, nb1, and nb2 which indicateaverage degrees of polymerization are 4.5).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (B) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.40 to 3.55 (4H), 3.65 to 3.75 (2H), 3.75to 3.85 (4H), 4.00 to 4.15 (22H), 5.10 to 5.15 (2H), 5.25 to 5.30 (2H),5.85 to 5.95 (2H) ¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F),−78.5 (4F), −80.5 (4F), −91.0 to −88.5 (36F)

Example 3

The compound represented by Formula (C) was obtained by the followingmethod.

The same operation as in Example 2 was performed except that thecompound represented by the following Formula (6ca) was used in place ofthe compound represented by Formula (6ba) to obtain 8.5 g of a compound(C) (in Formula (C), mc1, mc2, nc1, and nc2 which indicate averagedegrees of polymerization are 4.5).

(in Formula (6ca), THP represents a tetrahydropyranyl group).

Here, the compound represented by Formula (6ca) was synthesized byprotecting the secondary hydroxyl group of glycerin diglycidyl etherusing dihydropyran and then performing a mono addition reaction withallyl alcohol.

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (C) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.40 to 3.55 (4H), 3.65 to 3.75 (2H), 3.75to 3.85 (4H), 4.00 to 4.15 (27H), 5.10 to 5.15 (2H), 5.25 to 5.30 (2H),5.85 to 5.95 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 4

The compound represented by Formula (D) was obtained by the followingmethod.

The same operation as in Example 2 was performed except thatepibromohydrin was used in place of the compound represented by Formula(17) to obtain 5.8 g of a compound (D) (in Formula (D), md1, md2, nd1,and nd2 which indicate average degrees of polymerization are 4.5).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (D) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.40 to 3.55 (4H), 3.65 to 3.75 (2H)·3.75 to3.85 (4H)·4.0) to 4.15 (27H), 5.10 to 5.15 (2H), 5.25 to 5.30 (2H), 5.85to 5.95 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 5

The compound represented by Formula (E) was obtained by the followingmethod.

The same operation as in Example 1 was performed except that thecompound represented by the following Formula (7b-2a) was used in placeof the compound represented by Formula (6a) to obtain 6.1 g of acompound (Fi) (in Formula (E), me1, me2, ne1, and ne2 which indicateaverage degrees of polymerization are 4.5).

(in Formula (7b-2a). THP represents a tetrahydropyranyl group).

Here, the compound represented by Formula (7b-2a) was synthesized usingthe following method. Two molecules of 3-buten-1-ol were added toepibromohydrin and thus a compound having two butenyl groups and ahydroxyl group was synthesized. Then, the secondary hydroxyl group ofthe synthesized compound having two butenyl groups and a hydroxyl groupwas protected using dihydropyran, and a butenyl group was mono-oxidizedto obtain an epoxy compound having a butenyl group represented byFormula (7b-2a).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (E) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=1.60 to 1.80 (4H), 2.40 (4H), 3.40 to 4.20(37H), 5.10 to 5.30 (4H), 5.85 to 5.95 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 61

The compound represented by Formula (F) was obtained by the followingmethod.

The same operation as in Example 1 was performed except that thecompound represented by the following Formula (8ba) was used in place ofthe compound represented by Formula (6a) to obtain 5.9 g of a compound(F) (in Formula (F), mf1, mf2, nf1, and nf2 which indicate averagedegrees of polymerization are 4.5).

(in Formula (8ba), THP represents a tetrahydropyranyl group).

Here, the compound represented by Formula (8ba) was synthesized usingthe following method. One molecule of 4-pentene-1-ol and one molecule ofepibromohydrin were reacted to synthesize a compound, and the obtainedcompound was hydrolyzed. The primary hydroxyl group of the obtainedhydrolyzed compound was protected with a t-butyldimethylsilyl group, andthe secondary hydroxyl group was protected with a tetrahydropyranylgroup using dihydropyran. The t-butyldimethylsilyl group was deprotectedfrom the obtained compound, and the generated primary hydroxyl group andepibromohydrin were reacted to obtain an epoxy compound having apentenyl group represented by Formula (8ba).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (F) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=1.20 to 1.40 (4H), 2.40 (4H), 3.40 to 4.20(37H), 5.10 to 5.30 (4H), 5.85 to 5.95 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 71

The compound represented by Formula (G) was obtained by the followingmethod.

The same operation as in Example 1 was performed except that thecompound represented by the following Formula (9ba) was used in place ofthe compound represented by Formula (6a) to obtain 5.5 g of a compound(G) (in Formula (G), mg1, mg2, ng1, and ng2 which indicate averagedegrees of polymerization are 4.5).

(in Formula (9ba), THP represents a tetrahydropyranyl group).

Here, the compound represented by Formula (9ba) was synthesized usingthe following method. One molecule of 2-propyn-1-ol and one molecule ofepibromohydrin were reacted to synthesize a compound, and the obtainedcompound was hydrolyzed. The primary hydroxyl group of the obtainedhydrolyzed compound was protected with a t-butyldimethylsilyl group, andthe secondary hydroxyl group was protected with a tetrahydropyranylgroup using dihydropyran. The t-butyldimethylsilyl group was deprotectedfrom the obtained compound, and the generated primary hydroxyl group andepibromohydrin were reacted to obtain an epoxy compound having apropargyl group represented by Formula (9ba).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (G) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=2.45 (2H), 3.40 to 4.20 (37H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 8

The compound represented by Formula (H) was obtained by the followingmethod.

The same operation as in Example 1 was performed except that thecompound represented by Formula (10a) was used in place of the compoundrepresented by Formula (6a) to obtain 6.2 g of a compound (H) (inFormula (H), mh1, mh2, nh1, and nh2 which indicate average degrees ofpolymerization are 4.5).

Here, the compound represented by Formula (10a) was synthesized byreacting 2-thiopheneethanol with epibromohydrin.

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (H) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.10 to 3.15 (4H), 3.40 to 4.20 (27H), 6.80to 6.85 (4H), 7.05 to 7.10 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 9

The compound represented by Formula (1) was obtained by the followingmethod.

The same operation as in Example 1 was performed except that thecompound represented by Formula (11a) was used in place of the compoundrepresented by Formula (6a) to obtain 6.3 g of a compound (1) (inFormula (1), mi1, mi2, ni1, and ni2 which indicate average degrees ofpolymerization are 4.5).

Here, the compound represented by Formula (11a) was synthesized byreacting 1-methylpyrazole-5-methanol with epibronohydrin.

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (1) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.00 (6H), 3.40 to 4.60 (27H), 6.60 (2H),7.30 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 10

The compound represented by Formula (J) was obtained by the followingmethod.

The same operation as in Example 1 was performed except that thecompound represented by Formula (12a) was used in place of the compoundrepresented by Formula (6a) to obtain 6.3 g of a compound (J) (inFormula (J), mj1, mj2, nj1, and nj2 which indicate average degrees ofpolymerization are 4.5).

Here, the compound represented by Formula (12a) was synthesized byreacting methylthiazole ethanol with epibromohydrin.

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (J) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=2.35 to 2.40 (6H), 3.00 to 3.10 (4H), 3.40to 4.60 (27H), 8.45 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 11

The compound represented by Formula (K) was obtained by the followingmethod.

The same operation as in Example 2 was performed except that anintermediate synthesized in the same manner as in the compoundrepresented by Formula (17) using the compound represented by Formula(18) in place of the compound represented by Formula (16) was used inplace of the compound represented by Formula (17), and an intermediatesynthesized in the same manner as in the compound represented by Formula(18) using the compound represented by Formula (7b-2a) in place of thecompound represented by Formula (6ba) was used in place of the compoundrepresented by Formula (18) to obtain 5.8 g of a compound (K) (inFormula (K), mk1, mk2, nk1, and nk2 which indicate average degrees ofpolymerization are 4.5).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (K) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=1.60 to 1.80 (2H), 2.40 (2H), 3.40 to 4.20(37H), 5.10 to 5.30 (4H), 5.85 to 5.95 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 12

The compound represented by Formula (L) was obtained by the followingmethod.

The same operation as in Example 2 was performed except that anintermediate synthesized in the same manner as in the compoundrepresented by Formula (17) using the compound represented by Formula(18) in place of the compound represented by Formula (16) was used inplace of the compound represented by Formula (17), and an intermediatesynthesized in the same manner as in the compound represented by Formula(18) using the compound represented by the following Formula (19) inplace of the compound represented by Formula (6ba) was used in place ofthe compound represented by Formula (18) to obtain 6.1 g of a compound(L) (in Formula (L), ml1, ml2, nl1, and nl2 which indicate averagedegrees of polymerization are 4.5).

Here, the compound represented by Formula (19) was synthesized by anaddition reaction of epibromohydrin to phenol.

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (L) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.40 to 4.60 (30H), 5.10 to 5.15 (1H), 5.25to 5.30 (1H), 5.85 to 5.95 (1H), 6.90 (5H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 13

The compound represented by Formula (M) was obtained by the followingmethod.

The same operation as in Example 2 was performed except that anintermediate synthesized in the same manner as in the compoundrepresented by Formula (17) using the compound represented by Formula(18) in place of the compound represented by Formula (16) was used inplace of the compound represented by Formula (17), and an intermediatesynthesized in the same manner as in the compound represented by Formula(18) using the compound represented by Formula (10a) in place of thecompound represented by Formula (6ba) was used in place of the compoundrepresented by Formula (18) to obtain 7.1 g of a compound (M) (inFormula (M), mm1, mm2, nm1, and nm2 which indicate average degrees ofpolymerization are 4.5).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (M) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.10 to 3.15 (2H), 3.40 to 4.60 (32H), 5.10to 5.15 (1H), 5.25 to 5.30 (1H), 5.85 to 5.95 (1H), 6.80 to 6.85 (2H),7.05 to 7.10 (1H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F),−78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 14

The compound represented by Formula (N) was obtained by the followingmethod.

The same operation for the compound represented by Formula (16) inExample 1 was performed except that the compound represented by Formula(19) was used in place of the compound represented by Formula (6a) toobtain a compound represented by the following Formula (20) as anintermediate.

(in Formula (20), m which indicates an average degree of polymerizationis 4.5, and n which indicates an average degree of polymerization is4.5)

The same operation as in Example 2 was performed except that anintermediate synthesized in the same manner as in the compoundrepresented by Formula (17) using the compound represented by Formula(20) in place of the compound represented by Formula (16) was used inplace of the compound represented by Formula (17), and an intermediatesynthesized in the same manner as in the compound represented by Formula(18) using the compound represented by Formula (10a) in place of thecompound represented by Formula (6ba) was used in place of the compoundrepresented by Formula (18) to obtain 5.4 g of a compound (N) (inFormula (N), mn1, mn2, nn1, and nn2 which indicate average degrees ofpolymerization are 4.5).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (N) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.10 to 3.15 (2H), 3.40 to 4.60 (25H), 6.80to 7.00 (7H), 7.05 to 7.10 (1H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−55.5 to −51.5 (18F), −78.5 (4F), −80.5(4F), −91.0 to −88.5 (36F)

Example 15

The compound represented by Formula (D) was obtained by the followingmethod.

The same operation as in Example 1 was performed except that a compound(a number-average molecular weight of 1,000 and a molecular weightdistribution of 1.1) represented byHOCH₂CF₂O(CF₂CF₂O)_(md)(CF₂O)_(nd)CF₂CH₂OH (in the formula, md whichindicates an average degree of polymerization is 7.0, and nd whichindicates an average degree of polymerization is 0) was used in place ofthe compound (a number-average molecular weight of 1,000 and a molecularweight distribution of 1.1) represented byHOCH₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CH₂OH (in the formula, m whichindicates an average degree of polymerization is 4.5, and n whichindicates an average degree of polymerization is 4.5), and the compoundrepresented by Formula (6ba) was used in place of the compoundrepresented by Formula (6a) in Example 1 to obtain 8.4 g of a compound(D) (in Formula (D), md1 and md2 which indicate average degrees ofpolymerization are 7.0, and nd1 and nd2 which indicate average degreesof polymerization are 0).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (D) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.40 to 3.55 (4H), 3.65 to 3.75 (2H), 3.75to 3.85 (4H), 4.00 to 4.15 (27H), 5.10 to 5.15 (2H), 5.25 to 5.30 (2H),5.85 to 5.95 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−78.5 (4F), −81.3 (4F), −90.0 to −88.5(56F)

Example 16

The compound represented by Formula (O) was obtained by the followingmethod.

The same operation as in Example 1 was performed except that a compound(a number-average molecular weight of 1,000 and a molecular weightdistribution of 1.1) represented byHOCH₂CF₂CF₂O(CF₂CF₂CF₂O)_(p)CF₂CF₂CH₂OH (in the formula, p whichindicates an average degree of polymerization is 4.5) was used in placeof the compound (a number-average molecular weight of 1,000 and amolecular weight distribution of 1.1) represented byHOCH₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CH₂OH (in the formula, m whichindicates an average degree of polymerization is 4.5, and n whichindicates an average degree of polymerization is 4.5), and the compoundrepresented by Formula (6ba) was used in place of the compoundrepresented by Formula (6a) in Example 1 to obtain 7.5 g of a compound(O) (in Formula (O), po1 and po2 which indicate average degrees ofpolymerization are 4.5).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (O) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.40 to 3.55 (4H), 3.65 to 3.75 (2H), 3.75to 3.85 (4H), 4.00 to 4.15 (27H), 5.10 to 5.15 (2H), 5.25 to 5.30 (2H),5.85 to 5.95 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−84.0 to −83.0 (36F), −86.4 (8F), −124.3(8F), −130.0 to −129.0 (18F)

Example 171

The compound represented by Formula (P) was obtained by the followingmethod.

The same operation as in Example 1 was performed except that a compound(a number-average molecular weight of 1,000 and a molecular weightdistribution of 1.1) represented byHOCH₂CF₂CF₂CF₂O(CF₂CF₂CF₂CF₂O)_(q)CF₂CF₂CF₂CH₂OH (in the formula, qwhich indicates an average degree of polymerization is 3.0) was used inplace of the compound (a number-average molecular weight of 1,000 and amolecular weight distribution of 1.1) represented byHOCH₂CF₂O(CF₂CF₂O)_(m)(CF₂O)_(n)CF₂CH₂OH (in the formula, m whichindicates an average degree of polymerization is 4.5, and n whichindicates an average degree of polymerization is 4.5), and the compoundrepresented by Formula (6ba) was used in place of the compoundrepresented by Formula (6a) in Example 1 to obtain 5.3 g of a compound(P) (in Formula (P), qp1 and qp2 which indicate average degrees ofpolymerization are 3.0).

¹H-NMR and ¹⁹F-NMR measurements of the obtained compound (P) wereperformed, and the structure was identified from the following results.

¹H-NMR (acetone-D₆): δ[ppm]=3.40 to 3.55 (4H), 3.65 to 3.75 (2H), 3.75to 3.85 (4H), 4.00 to 4.15 (27H), 5.10 to 5.15 (2H), 5.25 to 5.30 (2H),5.85 to 5.95 (2H)

¹⁹F-NMR (acetone-D₆): δ[ppm]=−84.0 to −83.0 (32F), −122.5 (8F), −126.0(24F), −129.0 to −128.0 (8F)

Table 1 shows the structure of R¹, the structure of R² (a and Y¹ inFormula (2-1)), the structure of R³ (b and c in Formula (3), d inFormula (4), and e in Formula (5)), the structure of R⁴ (a and Y¹ inFormula (2-1)), and the structure of R⁵, when the compounds of Examples1 to 17 obtained in this manner were applied to Formula (1). In all ofthe compounds. Y² in Formula (2-1) representing R² and R⁴ is —O—.

TABLE 1 R² R⁴ a in Y¹ in b and c in Formula a in Y¹ in Formula Formula(3), d in Formula (4), Formula Formula Compound R¹ (2-1) (2-1) R³ and ein Formula (5) (2-1) (2-1) R⁵ Example 1 (A) allyl group 0 — Formula (3)4.5 0 — same as R¹ Example 2 (B) allyl group 0 — Formula (3) 4.5 1 —O—same as R¹ Example 3 (C) allyl group 0 — Formula (3) 4.5 2 —O— same asR¹ Example 4 (D) allyl group 1 —O— Formula (3) 4.5 1 —O— same as R¹Example 5 (E) 3-butenyl group 1 —OCH₂— Formula (3) 4.5 1 —OCH₂— same asR¹ Example 6 (F) 4-pentenyl group 1 —O— Formula (3) 4.5 1 —O— same as R¹Example 7 (G) propargyl group 1 —O— Formula (3) 4.5 1 —O— same as R¹Example 8 (H) thienylethyl group 0 — Formula (3) 4.5 0 — same as R¹Example 9 (I) methylpyrazolyl- 0 — Formula (3) 4.5 0 — same as R¹ methylgroup Example 10 (J) methylthiazole- 0 — Formula (3) 4.5 0 — same as R¹ethyl group Example 11 (K) allyl group 1 —O— Formula (3) 4.5 1 —OCH₂—3-butenyl group Example 12 (L) allyl group 1 —O— Formula (3) 4.5 0 —phenyl group Example 13 (M) allyl group 1 —O— Formula (3) 4.5 0 —thienylethyl group Example 14 (N) phenyl group 0 — Formula (3) 4.5 0 —thienylethyl group Example 15 (D) allyl group 1 —O— Formula (3) b = 7.0,c = 0 1 —O— same as R¹ Example 16 (O) allyl group 1 —O— Formula (4) 4.51 —O— same as R¹ Example 17 (P) allyl group 1 —O— Formula (5) 3.0 1 —O—same as R¹

[Comparative Example 1][Comparative Example 2]

The compound represented by the following Formula (T) was synthesized bythe method described in Patent Document 1.

(in Formula (T), mt1 and mt2 which indicate average degrees ofpolymerization are 7.0).

[Comparative Example 3][Comparative Example 4]

The compound represented by the following Formula (U) was synthesized bythe method described in Patent Document 2.

[Comparative Example 5][Comparative Example 6]

The compound represented by the following Formula (V) was synthesized bythe method described in Patent Document 2.

Comparative Example 7

The compound represented by the following Formula (W) was synthesized bythe method described in Patent Document 3.

Comparative Example 8

The compound represented by the following Formula (X) was synthesized bythe method described in Patent Document 4.

(in Formula (U), mu1, mu2, nu1, and nu2 which indicate average degreesof polymerization are 4.5).

(in Formula (V), pv1 and pv2 which indicate average degrees ofpolymerization are 4.5).

(in Formula (W), mw and nw which indicate average degrees ofpolymerization are 10.0), and

(in Formula (X), mx and nx which indicate average degrees ofpolymerization are 10.0).

Comparative Example 9

The compound represented by the following Formula (Y) was synthesized bythe method described in Patent Document 5.

(in Formula (Y), my and ny which indicate average degrees ofpolymerization are 10.0).

Comparative Example 10

The compound represented by the following Formula (Z) was synthesized bythe method described in Patent Document 2.

(in Formula (Z), mz and nz which indicate average degrees ofpolymerization are 10.0).

Next, solutions for forming a lubricating layer were prepared using thecompounds obtained in Examples 1 to 17 and Comparative Examples 1 to 10by the following method. Then, a lubricating layer of a magneticrecording medium was formed using the obtained solution for forming alubricating layer by the following method to obtain magnetic recordingmedia of Examples 1 to 17 and Comparative Examples 1 to 10.

“Solution for Forming Lubricating Layer”

The compounds obtained in Examples 1 to 17 and Comparative Examples 1 to10 were dissolved in Vertrel (registered trademark) XF (product name,commercially available from Du Pont-Mitsui Fluorochemicals Co., Ltd.) asa fluorine-based solvent, and diluted with Vertrel XF such that the filmthickness became 9.0 Å when applied onto the protective layer, and usedas solutions for forming a lubricating layer.

“Magnetic Recording Medium”

A magnetic recording medium in which an adhesive layer, a soft magneticlayer, a first underlayer, a second underlayer, a magnetic layer, and aprotective layer were sequentially provided on a substrate having adiameter of 65 nm was prepared. The protective layer was made of carbon.

The solutions for forming a lubricating layer of Examples 1 to 17 andComparative Examples 1 to 10 were applied by a dipping method onto theprotective layer of the magnetic recording medium, in which respectivelayers up to the protective layer were formed. Here, the dipping methodwas performed under conditions of an immersion speed of 10 mm/sec, animmersion time of 30 sec, and a lifting speed of 1.2 mm/sec.

Then, the magnetic recording medium to which the solution for forming alubricating layer was applied was put into a thermostatic chamber, aheat treatment for improving the adhesion between the protective layerand the lubricating layer was performed at a thermostatic chambertemperature (heat treatment temperature) shown in Table 2 and Table 3for 10 minutes, and thus the lubricating layer was formed on theprotective layer to obtain a magnetic recording medium.

The film thickness of the lubricating layer of the magnetic recordingmedia of Examples 1 to 17 and Comparative Examples 1 to 10 obtained inthis manner was measured using FT-1R (product name: Nicolet iS50,commercially available from Thermo Fisher Scientific). The results areshown in Table 2 and Table 3.

In addition, Table 2 and Table 3 show the number-average molecularweight (Mn) of the compounds of Examples 1 to 17 and ComparativeExamples 1 to 10.

TABLE 2 Number- Thermostatic average chamber Film Bond Wear Amountmolecular temperature thickness ratio resistance of Si ComprehensiveCompound weight (° C.) (Å) (%) test adsorbed evaluation Example 1 (A)2279 140 9.0 60 A 0.82 A Example 2 (B) 2353 140 9.0 65 A 0.77 A Example3 (C) 2427 140 9.0 70 A 0.75 A Example 4 (D) 2427 140 9.0 70 A 0.72 AExample 5 (E) 2483 140 9.0 70 A 0.69 A Example 6 (F) 2483 140 9.0 70 A0.63 A Example 7 (G) 2423 140 9.0 70 A 0.64 A Example 8 (H) 2419 140 9.070 A 0.68 A Example 9 (I) 2387 140 9.0 70 A 0.68 A Example 10 (J) 2449140 9.0 70 A 0.61 A Example 11 (K) 2455 140 9.0 65 A 0.68 A Example 12(L) 2389 140 9.0 65 A 0.68 A Example 13 (M) 2423 140 9.0 70 A 0.69 AExample 14 (N) 2385 140 9.0 65 A 0.62 A Example 15 (D) 2413 140 9.0 70 A0.70 A Example 16 (O) 2483 140 9.0 70 A 0.65 A Example 17 (P) 2485 1409.0 70 A 0.67 A

TABLE 3 Number- Thermostatic average chamber Film Bond Wear Amountmolecular temperature thickness ratio resistance of Si ComprehensiveCompound weight (° C.) (Å) (%) test adsorbed evaluation Comparative (T)2052 140 9.0 80 C 1.00 C Example 1 Comparative (T) 2052 100 9.0 70 B1.22 C Example 2 Comparative (U) 2198 140 9.0 80 C 1.06 C Example 3Comparative (U) 2198 100 9.0 70 B 1.27 C Example 4 Comparative (V) 2341140 9.0 80 C 1.15 C Example 5 Comparative (V) 2332 100 9.0 75 C 1.30 CExample 6 Comparative (W) 2298 140 9.0 60 C 1.25 C Example 7 Comparative(X) 2375 140 9.0 65 C 1.13 C Example 8 Comparative (Y) 2367 160 9.0 65 B1.21 C Example 9 Comparative (Z) 2146 140 9.0 70 D 1.50 D Example 10(Measurement of adhesion between the lubricating layer and theprotective layer (bond ratio))

The magnetic recording medium in which the lubricating layer was formedwas washed by a method of immersing it in Vertrel XF as a solvent for 10minutes, and lifting. The speed at which the magnetic recording mediumwas immersed in the solvent was 10 mm/sec, and the lifting speed was 1.2mm/sec.

Then, the film thickness of the lubricating layer was measured by thesame method used to measure the film thickness of the lubricating layerbefore washing.

Then, the film thickness of the lubricating layer before washing was setas A, the film thickness of the lubricating layer after washing (afterimmersion in the solvent) was set as B, and the binding ratio (bondratio) of the lubricant was calculated from a ratio of A and B((B/A)×100(%)). The results are shown in Table 2 and Table 3.

In addition, the following wear resistance test and chemical substanceresistance test were performed on the magnetic recording media ofExamples 1 to 17 and Comparative Examples 1 to 10.

(Wear Resistance Test)

Using a pin-on disc-type friction wear tester, an alumina sphere havinga diameter of 2 mm as a contact was slid on the lubricating layer of themagnetic recording medium at a load of 40 gf and a sliding speed of 0.25m/sec, and the friction coefficient of the surface of the lubricatinglayer was measured. Then, the sliding time until the frictioncoefficient of the surface of the lubricating layer rapidly increasedwas measured. The sliding time until the friction coefficient rapidlyincreased was measured four times for the lubricating layer of eachmagnetic recording medium, and the average value (time) thereof was usedas an index of the wear resistance of a lubricant coating.

Table 2 and Table 3 show the results of the magnetic recording mediausing the compounds of Examples 1 to 17 and the compounds of ComparativeExamples 1 to 10. The evaluation of the wear resistance based on thesliding time until the friction coefficient rapidly increased was asfollows.

A (excellent): 650 sec or longer

B (good): 550 sec or longer and shorter than 650 sec

C (acceptable): 450 sec or longer and shorter than 550 sec

D (unacceptable): shorter than 450 sec

Here, the time until the friction coefficient rapidly increased could beused as an index of the wear resistance of the lubricating layer for thefollowing reasons. This is because wear of the lubricating layer of themagnetic recording medium proceeds when the magnetic recording medium isused, and when the lubricating layer disappears due to wear, the contactand the protective layer come into direct contact with each other, andthe friction coefficient rapidly increases. The time until the frictioncoefficient rapidly increases is thought to be correlated with thefriction test.

(Chemical Substance Resistance Test)

The contamination of the magnetic recording medium due to environmentalsubstances that produced contamination substances in a high temperatureenvironment was examined by the following method. Si ions were used asthe environmental substances, and the amount of Si adsorbed was measuredas the amount of the contamination substances that contaminated themagnetic recording medium produced from the environmental substances.

Specifically, the magnetic recording medium to be evaluated was heldunder a high temperature environment with a temperature of 85° C., and ahumidity of 0% in the presence of siloxane-based Si rubber for 240hours. Next, the amount of Si adsorbed present on the surface of themagnetic recording medium was analyzed and measured using secondary-ionmass spectrometry (SIMS), and the degree of contamination with Si ionswas evaluated as the amount of Si adsorbed. The amount of Si adsorbedwas evaluated using a numerical value which is obtained when the resultof Comparative Example 1 was set to 1.00. The results are shown in Table2 and Table 3.

Then, the magnetic recording media of Examples 1 to 17 and ComparativeExamples 1 to 10 were comprehensively evaluated based on the followingcriteria. The results are shown in Table 2 and Table 3.

A (excellent): The time until the friction coefficient rapidly increasedwas 650 sec or longer, and the amount of Si adsorbed was less than 0.90

B (good): The time until the friction coefficient rapidly increased was550 sec or longer and shorter than 650 sec, and the amount of Siadsorbed was 0.90 or more and less than 1.00

C (acceptable): The time until the friction coefficient rapidlyincreased was 450 sec or longer and shorter than 650 sec, and the amountof Si adsorbed was 1.00 or more and less than 1.40

D (unacceptable): The time until the friction coefficient rapidlyincreased was shorter than 450 sec, and the amount of Si adsorbed was1.40 or more

As shown in Table 2, all of the magnetic recording media of Examples 1to 17 had a bond ratio of 60% or more, and had a comprehensiveevaluation of “A (excellent).” Accordingly, it was confirmed that thelubricating layers of the magnetic recording media of Examples 1 to 17had excellent adhesion and favorable chemical substance resistance andwear resistance even if the thickness was thin.

In addition, based on the results of Examples 1 to 3, it was confirmedthat, when a compound having a large total number of hydroxyl groupscontained in the structure of R² and R⁴ in Formula (1) was used, thebond ratio was high, the adhesion became favorable, the amount of Siadsorbed was small, and the chemical substance resistance becamefavorable.

On the other hand, as shown in Table 3, in Comparative Examples 1 and 3using a compound in which a glycerin structure was disposed in thecenter of the chain structure, a perfluoropolyether chain and a terminalgroup having two hydroxyl groups were bonded in that order to bothsides, and hydroxyl groups were disposed at both end terminals of thechain structure, the bond ratio was 80%, and the adhesion was higherthan in Examples 1 to 17. However, in Comparative Examples 1 and 3,since the adhesion was too strong, the lubricity of the lubricatinglayer was impaired, and the result of the wear resistance test was “C(acceptable).”

In addition, in Comparative Examples 2 and 4 in which the same compoundsas in Comparative Examples 1 and 3 was used, and the adhesion wasweakened by lowering the heat treatment temperature (thermostaticchamber temperature), the result of the wear resistance test was “B(good).” but the amount of Si adsorbed was large. This was speculated tobe because hydroxyl groups which were included in the compound but notinvolved in binding to the active sites on the protective layerattracted the environmental substances, which produce contaminationsubstances, to the lubricating layer.

In Comparative Example 5 using a compound in which an alkyl chain havingtwo hydroxyl groups was disposed in the center of the chain structure, aperfluoropolyether chain and a terminal group having two hydroxyl groupswere bonded in that order to both sides, and hydroxyl groups weredisposed at both end terminals of the chain structure, the bond ratiowas 80%, and the adhesion was higher than in Examples 1 to 17. However,in Comparative Example 5, since the adhesion was too strong, thelubricity of the lubricating layer was impaired, the result of the wearresistance test was “C (acceptable).” and the amount of Si adsorbed waslarge. This was speculated to be because two hydroxyl groups disposed inthe center were linked by an alkyl chain, and therefore the flexibilityof the entire molecule was insufficient. In addition, in ComparativeExample 5, it was speculated to be because hydroxyl groups which wereincluded in the compound but not involved in binding to the active siteson the protective layer attracted the environmental substances, whichproduce contamination substances, to the lubricating layer.

In addition, in Comparative Example 6 in which the same compound as inComparative Example 5 was used, and the adhesion was weakened bylowering the heat treatment temperature (thermostatic chambertemperature), the result of the wear resistance test was “C(acceptable).” and the amount of Si adsorbed was large. This wasspeculated to be because the fluorine-containing ether compoundcontained 6 hydroxyl groups, and therefore the bond ratio was notsufficiently lowered and was high as 75%, even if the heat treatmenttemperature (thermostatic chamber temperature) was lowered.

In addition, in Comparative Example 7 using a compound in which aperfluoropolyether chain was disposed in the center of the chainstructure, and an aromatic hydrocarbon was disposed at both terminals,the bond ratio was 60%, the result of the wear resistance test was “C(acceptable).” and the amount of Si adsorbed was larger than in Examples1 to 17.

In addition, in Comparative Example 8 using a compound in which aperfluoropolyether chain was disposed in the center of the chainstructure, and an allyl group was disposed at both terminals via twolinking groups having hydroxyl groups, the bond ratio was 65%, theresult of the wear resistance test was “C (acceptable).” and the amountof Si adsorbed was larger than in Examples 1 to 17.

In addition, in Comparative Example 9 using a compound in which aperfluoropolyether chain was disposed in the center of the chainstructure, and an aromatic heterocycle was disposed at both terminals,the bond ratio was 65%, the result of the wear resistance test was “B(good).” and the amount of Si adsorbed was larger than in Examples 1 to17.

This was speculated to be because the compounds used in ComparativeExamples 7 to 9 did not have a glycerin structure in the center of thechain structure, and therefore an effect of improving the adhesion bythe bond between the hydroxyl group disposed in the center of the chainstructure and the protective layer was not obtained.

In addition, in Comparative Example 10 using a compound in which aperfluoropolyether chain was disposed in the center of the chainstructure, a terminal group having two hydroxyl groups was bonded toboth sides, and hydroxyl groups were disposed at both end terminals ofthe chain structure, the result of the wear resistance test was “D(unacceptable).” and the amount of Si adsorbed was larger than inExamples 1 to 17.

Industrial Applicability

When the lubricant for a magnetic recording medium containing thefluorine-containing ether compound of the present invention is used, itis possible to form a lubricating layer having excellent adhesion andfavorable chemical substance resistance and wear resistance even if thethickness is thin.

REFERENCE SIGNS LIST

-   10 Magnetic recording medium-   11 Substrate-   12 Adhesive layer-   13 Soft magnetic layer-   14 First underlayer-   15 Second underlayer-   16 Magnetic layer-   17 Protective layer-   18 Lubricating layer

1. A fluorine-containing ether compound represented by the followingFormula (1):R¹—R²—CH₂—R³—CH₂—OCH₂CH(OH)CH₂O—CH₂—R³—CH₂—R⁴—R⁵  (1) (in Formula (1),R³ represents a perfluoropolyether chain; R² and R⁴ represent a divalentlinking group having a polar group, and may be the same as or differentfrom each other, R¹ and R⁵ represent a terminal group bonded to anoxygen atom of R² or R⁴, and may be the same as or different from eachother; and at least one of R¹ and R⁵ is any one selected from the groupconsisting of an alkenyl group having 2 to 8 carbon atoms, an alkynylgroup having 3 to 8 carbon atoms, an aromatic hydrocarbon-containinggroup, and an aromatic heterocycle-containing group).
 2. Thefluorine-containing ether compound according to claim 1, wherein, inFormula (1), R¹ and R⁵ each represent an alkenyl group having 2 to 5carbon atoms or an alkynyl group having 3 to 5 carbon atoms.
 3. Thefluorine-containing ether compound according to claim 1, wherein, inFormula (1), R¹ and R⁵ are each independently any one selected from thegroup consisting of an allyl group, a 3-butenyl group, a 4-pentenylgroup, and a propargyl group.
 4. The fluorine-containing ether compoundaccording to claim 1, wherein, in Formula (1), R¹ and R⁵ are an aromaticheterocycle-containing group.
 5. The fluorine-containing ether compoundaccording to claim 1, wherein, in Formula (1), R¹ and R⁵ are eachindependently any one selected from the group consisting of a groupcontaining a thiophene ring, a group containing a thiazole ring, and agroup containing a pyrazole ring.
 6. The fluorine-containing ethercompound according to claim 1, wherein the polar group is a hydroxylgroup.
 7. The fluorine-containing ether compound according to claim 6,wherein, in Formula (1), a total number of a hydroxyl group contained inR² and a hydroxyl group contained in R⁴ is 2 to
 5. 8. Thefluorine-containing ether compound according to claim 1, wherein, inFormula (1), R² and R⁴ contain 1 to 3 linking groups represented by thefollowing Formula (2):—CH₂CH(OH)CH₂—  (2)
 9. The fluorine-containing ether compound accordingto claim 8, wherein, in Formula (1), R² and R⁴ are a linking grouprepresented by the following Formula (2-1):—O—X—(Y¹X)_(a)—Y²—  (2-1) (in Formula (2-1), a represents an integer of0 to 2; X represents Formula (2); Y¹ represents any one selected fromthe group consisting of —O—, —CH₂—, —CH₂O—, and —OCH₂—; and Y²represents —O— or —CH₂O—).
 10. The fluorine-containing ether compoundaccording to claim 9, wherein, in Formula (2-1), Y¹ and Y² are —O—. 11.The fluorine-containing ether compound according claim 1, wherein, inFormula (1), R³ is any one selected from the group consisting ofperfluoropolyether chains represented by the following Formulae (3) to(5):—CF₂—(OCF₂CF₂)_(b)—(OCF₂)_(c)—OCF₂—  (3) (in Formula (3), b and cindicate an average degree of polymerization, b represents 1 to 20, andc represents 0 to 20),—CF₂CF₂—(OCF₂CF₂CF₂)_(d)—OCF₂CF₂—  (4) (in Formula (4), d indicates anaverage degree of polymerization, and represents 1 to 20), and—CF₂CF₂CF₂—(OCF₂CF₂CF₂CF₂)_(e)—OCF₂CF₂CF₂—  (5) (in Formula (5), eindicates an average degree of polymerization, and represents 1 to 10).12. The fluorine-containing ether compound according to any claim 1,wherein, in Formula (1), R¹ and R⁵ are the same.
 13. Thefluorine-containing ether compound according to claim 1, wherein, inFormula (1), both R¹ and R⁵ are any one selected from the groupconsisting of an alkenyl group having 2 to 8 carbon atoms, an alkynylgroup having 3 to 8 carbon atoms, an aromatic hydrocarbon-containinggroup, and an aromatic heterocycle-containing group, R¹ and R⁵ aredifferent from each other, and at least one of R¹ and R⁵ is any oneselected from the group consisting of an allyl group, a 3-butenyl group,and a 4-pentenyl group.
 14. The fluorine-containing ether compoundaccording to claim 1, which is any of compounds represented by thefollowing Formulae (A) to (P):

(in Formula (A), ma1, ma2, na1, and na2 indicate an average degree ofpolymerization, ma1 and ma2 represent 1 to 20, and na1 and na2 represent0 to 20), (in Formula (B), mb1, mb2, nb1, and nb2 indicate an averagedegree of polymerization, mb1 and mb2 represent 1 to 20, and nb1 and nb2represent 0 to 20), (in Formula (C), mc1, mc2, nc1, and nc2 indicate anaverage degree of polymerization, mc1 and mc2 represent 1 to 20, and nc1and nc2 represent 0 to 20), and (in Formula (D), md1, md2, nd1, and nd2indicate an average degree of polymerization, md1 and md2 represent 1 to20, and nd1 and nd2 represent 0 to 20),

(in Formula (E), me1, me2, ne1, and ne2 indicate an average degree ofpolymerization, me1 and me2 represent 1 to 20, and ne1 and ne2 represent0 to 20), (in Formula (F), mf1, mf2, nf1, and nf2 indicate an averagedegree of polymerization, mf1 and mf2 represent 1 to 20, and nf1 and nf2represent 0 to 20), (in Formula (G), mg1, mg2, ng1, and ng2 indicate anaverage degree of polymerization, mg1 and mg2 represent 1 to 20, and ng1and ng2 represent 0 to 20), and (in Formula (H), mh1, mh2, nh1, and nh2indicate an average degree of polymerization, mh1 and mh2 represent 1 to20, and nh1 and nh2 represent 0 to 20),

(in Formula (1), mi1, mi2, ni1, and ni2 indicate an average degree ofpolymerization, mi1 and mi2 represent 1 to 20, and ni1 and ni2 represent0 to 20), (in Formula (J), mj1, mj2, nj1, and nj2 indicate an averagedegree of polymerization, mj1 and mj2 represent 1 to 20, and nj1 and nj2represent 0 to 20), (in Formula (K), mk1, mk2, nk1, and nk2 indicate anaverage degree of polymerization, mk1 and mk2 represent 1 to 20, and nk1and nk2 represent 0 to 20), and (in Formula (L), ml1, ml2, nl1, and nl2indicate an average degree of polymerization, ml1 and ml2 represent 1 to20, and nl1 and nl2 represent 0 to 20),

(in Formula (M), mm1, mm2, nm1, and nm2 indicate an average degree ofpolymerization, mm1 and mm2 represent 1 to 20, and nm1 and nm2 represent0 to 20), (in Formula (N), mn1, mn2, nn1, and nn2 indicate an averagedegree of polymerization, mn1 and mn2 represent 1 to 20, and nn1 and nn2represent 0 to 20), (in Formula (O), po1 and po2 indicate an averagedegree of polymerization, and each represent 1 to 20), and (in Formula(P), qp1 and qp2 indicate an average degree of polymerization, and eachrepresent 1 to 10).
 15. The fluorine-containing ether compound accordingto claim 1, wherein the number-average molecular weight thereof is in arange of 500 to 10,000.
 16. A lubricant for a magnetic recording medium,which contains the fluorine-containing ether compound according toclaim
 1. 17. A magnetic recording medium having at least a magneticlayer, a protective layer, and a lubricating layer sequentially providedon a substrate, wherein the lubricating layer contains thefluorine-containing ether compound according to claim
 1. 18. Themagnetic recording medium according to claim 17, wherein the averagefilm thickness of the lubricating layer is 0.5 nm to 2.0 nm.